Although I was very tired, _________.
A.but I helped to clear up the mess after the party
B.I helped to clear up the mess after the party
C.and I tried to clear up the mess after the party
D.I didn't help to clear up the mess after the party

I took off my shoes before entering the room _________.
A.in order to not dirty the floor
B.so that I not dirty the floor
C.in order not dirtying the floor
D.so as not to dirty the floor

The living conditions of the population _________in the past years.
A.has been improved
B.have been improved
C.improved
D.were improved

_________these plants regularly or they will die.
A.Water
B.If you water
C.Unless you water
D.Because you water

The government has classified 54 species of mammal and 60 species of birds in Vietnam today as being endangered.
A.has classified
B.mammal
C.birds
D.being endangered

You can use my phone if yours _________.
A.won't be worked
B.won't work
C.isn't worked
D.doesn't work

The strange disease_________to have originated in Africa.
A.thinks
B.is thinking
C.is thought
D.thought

Concern for the environment is now at the_________of many governments' policies.
A.core
B.aim
C.target
D.purpose

People tend to work hard at this_________of life.
A.distance
B.stage
C.space
D.level

A.vein
B.reign
C.foreign
D.main