介词填空 I'm looking for my pen __a long time,but I can't find it.

介词填空 I'm looking for my pen __a long time,but I can't find it.
介词填空 I'm looking for my pen __a long time,but I can't find it.

介词填空 I'm looking for my pen __a long time,but I can't find it.
介词填空 I'm looking for my pen _for_a long time,but I can't find it.

for a long time 很长时间
我找钢笔找了好久，但是找不到。

填for，for a long time表示一段时间，固定短语