Question

It was midningt ___they reached the camp side. A that B when C while D as

Answer 1

选B啊，把it
was
去掉即midnight
they
reached
the
camp
side
，要组成一个句子的话就要加一个介词at,而when是一个副词，所以要选B.
如果句子是It
was
at
midnight
____they
reached
the
camp
side.的话就要选A了，同样把it
was
和that去掉的话能组成一个句子，不需要添加任何介词，所以选A。