gwd28-21

i agree with u

a is right

me too.

E : "they " refers  unclearly."single locusts" or "locusts"

me too!

a is right!

28-21: 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,>>

B: when placing them with others of their species, then

>从句里的分词省略结构中 , 逻辑主语和主语不一志  placing  应用被动>

C: locusts, when placed with others of their species,

结构不明确  句中已有主语 they

D: placing them with others of their species,

用被动

E: placed with others of their species, then

从句没主语

E中：主从句逻辑主语一致时，可以省略（after,when等词引导的）从句 主语，这里如果+when are，应该可以

entomologists

single locusts

creatures

e中but前面有三个复数名词,指代不清,a更清晰