Tìm mệnh đề đúng trong các mệnh đề sau
A. Nếu hình H có trục đối xứng thì nó có ít nhất một tâm đối xứng.
B. Nếu hình H có mặt đối xứng thì nó có ít nhất một trục đối xứng.
C. Nếu hình H có mặt đối xứng và có trục đối xứng thì nó có ít nhất một tâm đối xứng.
D. Nếu hình H có mặt đối xứng và có tâm đối xứng nằm trên mặt đối xứng thì nó có ít nhất một tâm đối xứng.

Cho hình chóp $S.ABC$ có đáy là tam giác đều cạnh a. Các mặt bên$(SAB),\,(SAC)$ cùng vuông góc với mặt đáy$(ABC)$; góc giữa SB và mặt$(ABC)$ bằng${{60}^{0}}$. Tính thể tích khối chóp$S.ABC$.
A. $\frac{{3{{a}^{3}}}}{4}$ 
B. $\frac{{{{a}^{3}}}}{2}$ 
C. $\frac{{{{a}^{3}}}}{4}$ 
D. $\frac{{{{a}^{3}}}}{{12}}$

Khối đa diện lồi đều có số mặt nhiều nhất là
A. 12
B. 30
C. 8
D. 20

Cho hình chóp S.ABCD có đáy ABC là tam giác vuông cân tại A, cạnh $BC=a\sqrt{2}$, cạnh bên SA vuông góc với mặt phẳng đáy, mặt bên (SBC) tạo với mặt đáy (ABC) một góc bằng${{45}^{0}}$. Thể tích khối chóp S.ABC theo a bằng 
A. ${{V}_{{S.ABC}}}=\frac{{{{a}^{3}}\sqrt{2}}}{6}$ 
B. ${{V}_{{S.ABC}}}=\frac{{{{a}^{3}}\sqrt{2}}}{2}$ 
C. ${{V}_{{S.ABC}}}=\frac{{{{a}^{3}}\sqrt{2}}}{4}$ 
D. ${{V}_{{S.ABC}}}=\frac{{{{a}^{3}}\sqrt{2}}}{{12}}$

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.