D. to

18.It is necessary _______ a foreign language.

( B )

A. of college students to master

B. for college students to master

C. that college students master

D. that college students to master

19.Henry would never forget _______ his mother-in-law for the first

time. He was so pleased with the gifts she brought for him. ( C )

A. meet

B. to meet

C. meeting

D. met

20.Do you know the man _______ under the apple tree?

( C )

A. lay

B. lain

C. lying

D. laying

21._______ a reply, he decided to write again.

( C )

A. Not receiving

B. Receiving not

C. Not having received

D. Having not received