Does the HSK6 exam paper H61218 question 54 (语病) have a correct answer?

Question

This is a HSK6 语病 question, wherein precisely one sentence is ungrammatical in some way:

1. 昨天我从火车站出来的时候,天下了大雨。
2. 鲸的体形像鱼,但却是用肺呼吸、胎生的哺乳动物。
3. 伤害人的话语就像泼出去的水,一旦说出就永远无法收回。
4. 有个成语叫“熟能生巧”,这里的“巧”其实就是不断重复练习的结果。

_{HSK6 H61218 Q.54}

The given answer is 1, but three native speakers here and here didn't find any major issues with it; one wrote: 前句无介词（我不确定，严格说来要介词）. This makes me wonder if any of these sentences are ungrammatical. I don't see any errors myself.

Question: Does the HSK6 exam paper H61218 question 54 (语病) have a correct answer?

(PS. For precedent, the correct answer to H61008 Q.53 is B, but the official answer is C. So the answers are not infallible.)

Answer 1

The problem is with the aspect.

昨天我从火车站出来的时候 is a point of time, while 了 is a dynamic perfect particle. According to the context, the sentence is meant to say that it was raining when I got out of the train station yesterday. Thus 下了 should be changed to 下着 or 正在下.

It's wrong to say 严格说来要介词. At the sentence-initial position, the temporal phrase uses the unmarked form, i.e. a bare NP. Note that the unmarked temporal phrase should be thought as a separate form of temporal phrases, not as ellipsis of the coverb.

Answer 2

了 indicated completeness of the verb

昨天我从火车站出来的时候,天下了大雨。 Would mean the rain has stopped. It is incompatible with 的时候 (the time/ moment)

It should be 昨天我从火车站出来的时候,天(正)下著大雨。(It was raining at that moment) or 昨天我从火车站出来的时候,天下(起)了大雨。(it started raining at that moment)

Answer 3

I think the answer should be 2, instead of 1.

鲸的体形像鱼,但却是用肺呼吸、胎生的哺乳动物。

The topic is 鲸, not 鲸的体形. So, it should be something like:

鲸, (它的)体形像鱼,但却是用肺呼吸、胎生的哺乳动物。

Basically, it mixed up the subjects of 鲸 and 鲸的体形. It might be okay in spoken, but not in the formal writing.