Many strange new means of transport have been developed in our century, the strangest of _____ being perhaps the hovercraft(气垫船).

When I entered the room I found she was listening to the music with her face ___ in tears. 

 With him ______ the way, we had little trouble finding the school.

With so many people ______ in the mine(矿), none of the rescue workers would stop to have a rest.

Almost all of his time ______ experiments, he has no time to visit his parents.