A. is
B. was
C. has
D. were

A. do
B. did
C. does
D. done

A. are
B. were
C. was
D. be

A. explains
B. explained
C. explain
D. explaining

A. have
B. has
C. had
D. was

A. did
B. have
C. has
D. had

A. play
B. plays
C. played
D. playing

A. sings
B. singing
C. was singing
D. sing

A. take
B. takes
C. took
D. taken

A. rings
B. rang
C. ring
D. rung