问一道语法题

 According to entomologists,single locusts are quiet creatures,but when locusts are placed with others of their species,they become excited,change color,vibrate,and even hum.

A.when locusts are placed with others of their species,

E.placed with others of their species,then

答案是A, 想不通E为什么不对

A.when locusts are placed with others of their species,

===》According to entomologists,single locusts are quiet creatures,but when locusts are placed with others of their species,they become excited,change color,vibrate,and even hum.

E.placed with others of their species,then

==》According to entomologists,single locusts are quiet creatures,but placed with others of their species,then they become excited,change color,vibrate,and even hum.

1# 改变原句中心，将时间状语从句改成并列成分。

2# but 后面的句子明显不完整，如果认为placed 前面省略了single locusts 做主语的话，then they 前面需要加上and 连接两个分句。