I ______ sooner but I didn’t know that they were waiting for me.

A．had come

B．was coming

C．would come

D．would have come

目前直接利用太阳能的方式主要有两种：一种时光热转换，生活中常见的这种转换设备有太阳能热水器，它是把太阳能转换为______能的装置，二是光电转换，即把太阳能直接转换为电能，实际应用有______．