Cho hình chóp tam giác $S.ABC$ có$\displaystyle \widehat{{ASB}}=\widehat{{CSB}}={{60}^{0}},\,\widehat{{CSA}}={{90}^{0}},\,SA=SB=SC=2a$. Tính thể tích khối chóp$S.ABC$
A. $\frac{{{{a}^{3}}\sqrt{6}}}{3}$ 
B. $\frac{{2{{a}^{3}}\sqrt{6}}}{3}$ 
C. $\frac{{2{{a}^{3}}\sqrt{2}}}{3}$ 
D. $\frac{{{{a}^{3}}\sqrt{2}}}{3}$

Choose the correct sentence which is built from the words and phrases given:
Remember/ lock/ door/ go out.
A. You remember to lock the door before you go out.
B. Remember locking the door before going out.
C. Remember to lock the door before going out.
D. Remember to lock the door before you going out.

Choose the correct sentence which is built from the words and phrases given:
I hope / we / able / solve the problems / over population and pollution.
A. I hope whether we are able to solve the problems, those are over population and pollution.
B. I hope if we will be able to solve the problems, which are over population and pollution.
C. I hope that we will be able to solve the problems of over population and pollution.
D. I hope when we will be able to solve the problem for over population and pollution.

Choose the correct sentence which is built from the words and phrases given:
First / category / be / state / school / system / which / free / all / student / pay / by / state //.
A. First category is the state school system, which is free with all students, paying by the state.
B. The first category is the state school system, which is free to all students, paid for by the state.
C. The first category is the state school system, which free to all students is paying for by the state.
D. Firstly category of the state school system, which is free to all students and it is tobe paid for by the state.

Choose the correct sentence which is built from the words and phrases given:
Wood/ long/ popular/ building material/ North America.
A. Wood was long a popular building material in North America.
B. Wood had long been a popular building material in North America.
C. Wood have long been a popular building material in North America.
D. Wood has long been a popular building material in North America.

Choose the correct sentence which is built from the words and phrases given:
If/ he/ come/ station/ earlier/ not miss/ train.
A. If he had come to the station earlier he would not have missed the train.
B. If he have come to the station earlier he would not have missed the train.
C. If he had came to the station earlier he would not have missed the train.
D. If he had come to the station earlier he would have not missed the train.

Choose the correct sentence which is built from the words and phrases given:
you / conserve energy / go to school or to work by bus / turn off your electric devices / you are not using them
A. As you want to conserve energy, go to school or to work by bus and so turn off your electric devices when you are not using them.
B. If you want to conserve energy, go to school or to work by bus together with turn off your electric devices when you are not using them.
C. Suppose you want to conserve energy, go to school or to work by bus and turn off your electric devices when you are not using them.
D. When you want to conserve energy, you needn’t go to school or to work by bus and turn off your electric devices when you are not using them.

Choose the correct sentence which is built from the words and phrases given:
Interview/ you/ care/ appearance/ gather/ information/ company/ as/ can.
A. While being interviewed, you should neither take good care of your personal appearance nor gather as much information about the company as you can.
B. During the interview, you should either take good care of your personal appearance or gather as much information about the company as you can.
C.  Before the interview, you shouldn’t take good care of your personal appearance but gather as much information about the company as you can.
D. Before the interview, you should take good care of your personal appearance and gather as much information about the company as you can.

Choose the correct sentence which is built from the words and phrases given:
Development/ birth-control methods/ free/ cycle/ child bearing.
A. Since the development of effective birth-control methods, women were from the endless cycle of child bearing.
B. The development of effective birth-control methods freed women from the endless cycle of child bearing.
C. Thanks to the development of effective birth-control methods, women from the cycle of child bearing.
D. Since the development of effective birth-control methods, women had been set free from the cycle of child bearing.

Choose the correct sentence which is built from the words and phrases given:
Mary says/ she / put/ higher class.
A. Mary says she’d like to have been put in higher class.
B. Mary says she’d like to have put in higher class.
C. Mary says she’d like to put in higher class.
D. Mary says she would put in higher class.