Sentence improvement — Conditional tense sequencing: improve ‘‘I would have waited for you at the station if I knew that you would come.’’ to a standard third conditional form.

Given sentence
I would have waited for you at the station if I knew that you would come.

Concept/Approach
A third conditional (imagined past) takes: If + past perfect → would have + past participle. Therefore, ‘‘if I had known’’ is required to match ‘‘would have waited’’.

Correct pattern
If I had known (earlier), I would have waited (then).

Option analysis
A: had known — Correct past perfect for third conditional.B: was knowing — Progressive aspect is wrong; ‘‘know’’ is stative.C: have known — Present perfect mismatches the counterfactual past.D: No improvement — Keeps incorrect sequencing.

Final Answer
had known