题目内容：

___ I had finished my letter,I posted it.
A,During B,While C,When D,Until

优质解答

___ I had finished my letter,I posted it.
A,During B,While C,When D,Unti
选C
根据意思是当我写完信后,我把它寄了出去
during是在.期间的意思
until是知道的意思
when和while都是当的意思
这边强调先后,所以用when