Only after staying in England for a few weeks did Li Lei become used ____ Chinese. 

Newton was sitting under an apple tree ______ an apple fell onto his head. 

 _________ happened to be no one in the building when the fire broke out.

. ______ it rains when we can’t find a place to escape from the rain?

—— How did you pass the challenging test?—— It was a long time       I found a series of suitable methods.