I studied English for four years in high school. _______ had trouble talking with people when I was traveling in the US.
A.Therefore, I
B.Otherwise, I
C.Although I
D.However, I

_______in the atmosphere is the temperature falling below freezing.
A.Frost is produced
B.Frost produces
C.What produces frost
D.What is frost produced

He said that the plane had already left and that I _______ an hour earlier.
A.must have arrived
B.had to arrive
C.should have arrived
D.was supposed to arrive

Good teeth help us to ................
A.be nice
B.have a good eyesight
C.chew our food
D.be important

A lot of people visit a dentist only when ............
A.their teeth grow properly
B.they have holes in their teeth
C.they have toothache
D.they have brushed their teeth

There is a mistake in the sentence. Find the mistake and correct it.
Surface is many cheaper than airmail
A.Surface
B.many
C.cheaper
D.airmail

There is a mistake in the sentence. Find the mistake and correct it.
The climate in Vietnam is different than that in England.
A.The climate
B.different
C.than
D.in

She /used/ stay / her uncle/ when / be / a child.
A.She used to studying with her uncle when she was a child
B.She used to study with her uncle when she had been a child
C.She used to study with her uncle when she were a child
D.She used to study with her uncle when she was a child

It / difficult/ learn English / without/ good dictionary.
A.It is difficult to learn English without a good dictionary.
B.It is difficult for learning English without a good dictionary.
C.It is difficult of learning English without a good dictionary.
D.It is difficult from learning English without a good dictionary.

We ought to try clean our teeth ..............
A.once a day
B.at least twice a day
C.between meals
D.before breakfast