When the old man ______ to walk back to his house, the sun ______ itself behind the mountain.

A．started; had already hidden

B．was starting; hid

C．had started; had already hidden

D．had started; was hiding

右图为我国某城市月平均气温及月平均总辐射曲线图。完成下列问题。

该城市可能是（）

A．重庆

B．广州

C．天津

D．乌鲁木齐