When thrusters A, B, and D are on, the Fuel gauge glows and the Helium tank rattles.

当开启推进器 A、B 和 D 时，燃油量表闪烁发光并且氦气瓶发出咔嗒声。

So, A, B, and D are correct.

所以，A、B、D 正确。

When thrusters A, B, and D are on, the Fuel gauge glows and the Helium tank rattles.

2. 当推进器 A、B 和 D 开启时，燃料表发光， 氦气罐发出嘎嘎声。

When the relative pronoun represents the object of the relative clause, such as in sentences b) and d) , it can be left out.

当关系代词指定了定语从句中的宾语，比如第二句和第四句，它就可以被省略。

An exercise for s sounds, p sounds, c sounds, and to some extent, b and d as well.

s 音、p 音、c 音以及在某种程度上 b 和 d 音的练习。