The theory he stuck to ______ to be right later.[ ]

What are you going to when you grow up—I’m going to be a singer.

What were you doing when I called you at 8 p.m. yesterday —I the piano at that time.

Fuzhou Subway Line 1 is underconstruction,which______to be a big improvement for the local traffic jam.

The girlarranged to have piano lessons at the training centre with her sister________shewould stay for an hour