He jumped into the water when he heard a boy for help.

The weather turned out to be very good,________ was more than we could expect.

You should inspect the wheels regularly, and replace them ______ they cause you trouble

Guilin is famous ____ its beautiful hills and rivers, while Kunming is famous ____ the Spring City

The newlydiscovered star was named ________ a Chinese astronomer ________ honour of his contributions to astronomy.[ ]