问题补充：
They considered a computer, which was considered a great help in their work.
A. to buy; to be
B. buying; being
C. to buy; being
D. buying; to be
答案：
A. to buy; to be
B. buying; being
C. to buy; being
(答案→)D. buying; to be
解析：consider doing sth. 考虑做某事；considered to be被认为
