17.Three students ______ in this university come from the South.
a. of ten b. out of in ten c. out of ten d. in tens
18.Strings of the same thickness made of nylon are ______.
a. five times stronger than those b. five time stronger than those
b. five times strong than those d. five times stronger as those
19.the wheels of the old wagon are nearly ______ those of a modern car.
a. twice the size of b. twice size of c. twice sizes of d. twice the size of
20.One day on the moon is ______.
a. two Earth week long b. two Earth weeks long
b. two Earth weeks longer d. two Earth weeks length