______ cleans the blackboard is to be praised.

A. /; the

B. /; /

C. the; /

D. the; the

A. when

B. where

C. what

D. that

A. what to do it

B. how to do

C. what to do

D. to do what

A. when

B. where

C. that

D. which

A. that

B. which

C. the one

D. the one what

A. what

B. why

C. that

D. which

A. was written

B. be written

C. must be written

D. would be written

A. paid off

B. paid back

C. carried out

D. paid for

A. What; why

B. That; how

C. What; how

D. That; why

A. that

B. where

C. which

D. when