Experiments of this kind ___in both the U.S and Europe well before the Second World War. 
#102411
A
had conducted
B
have conducted
C
have been conducted
D
had been conducted
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By the time Jack returned home from England, his son            from college.
#101871
A
graduated
B
has graduated
C
had been
D
had graduated
—Sorry. I ________ to post the letter for you. —Never mind. ________ it myself after school. 
#104473
A
forget; I’d rather post
B
forgot; I’ll post
C
forgot; I’m going to post
D
forget; I’d better post