The old man often looked back on the past days ________ he worked hard to make a living.

A．which

B．when

C．where

D．that

千日红的观赏期较长，其原因主要是（）的缘故。

A、开花时间较长

B、苞片膜质可作“于花”观赏

C、分批播种

D、生长旺盛