18.

18.
Although the first pulsar,or rapidly spinning collapsed star,to be sighted was in the summer of 1967 by graduate student Jocelyn Bell,it had not been announced until February,1968.
(A) Although the first pulsar,or rapidly spinning collapsed star,to be sighted was in the summer of 1967 by graduate student Jocelyn Bell,it had not been announced until February,1968.
(B) Although not announced until February,1968,in the summer of 1967 graduate student Jocelyn Bell observed the first pulsar,or rapidly spinning collapsed star,to be sighted.
(C) Although observed by graduate student Jocelyn Bell in the summer of 1967,the discovery of the first sighted pulsar,or rapidly spinning collapsed star,had not been announced before February,1968.
(D) The first pulsar,or rapidly spinning collapsed star,to be sighted was observed in the summer of 1967 by graduate student Jocelyn Bell,but the discovery was not announced until February,1968.
(E) The first sighted pulsar,or rapidly spinning collapsed star,was not announced until February,1968,while it was observed in the summer of 1967 by graduate student Jocelyn Bell.
21.
Before scientists learned how to make a synthetic growth hormone,removing it painstakingly in small amounts from the pituitary glands of human cadavers.
(A) scientists learned how to make a synthetic growth hormone,removing it painstakingly
(B) scientists had learned about making a synthetic growth hormone,they had to remove it painstakingly
(C) scientists learned how to synthesize the growth hormone,it had to be painstakingly removed
(D) learning how to make a synthetic growth hormone,scientists had to remove it painstakingly
(E) learning how to synthesize the growth hormone,it had to be painstakingly removed by scientists
我选一个C,21D,21 C