16.
A. break
B. breakage
C. breakdown
D. breaking
17.
A. concerned with
B. concerning
C. concerning with
D. concerned for
18.
A. reaction
B. action
C. interaction
D. relation
19.
A. distributed
B. attributed
C. contributed
D. construed
20.
A. discover
B. uncover
C. recover
D. cover