The fact has worried many scientists _____ the earth is becoming warmer and warmer these years. [ ]

When asked about their opinion about the schoolmaster, many teachers would prefer to see him step aside _________younger men.[ ]

When I wanted to express my thanks to him，words ___ me. I just held his hands firmly and choked.

The driver drove __ hit a big tree and the car came to a stop

I ___ my son ___ a doctor, but he wasn’t good enough at science