The planet of Venus, which routinely revolves around the Sun in an ellipse, has many active volcanos. One of them is taller than Mount Everest.

A. volcanos, one of which

B. volcanos; there is one that

C. volcanos, and one

D. volcanos, such that one

Correct Answer is A. I marked C because I thought that A is grammatically incorrect as it turns out to be run on.

So, sentences with "of which" are relative clause too? Why A? Not C?

  • Was there a specific part of grammar that you are studying. A,B, and C are reasonably close in meaning to the original phrase.
    – James K
    Commented Feb 21, 2018 at 16:11

1 Answer 1


You state correctly in the title of your question that "one of which" would introduce a relative clause. If this is the topic that you are studying now, and the test was supposed to test your knowledge of this topic, then only "one of which" is correct, because

Relative clauses are clauses starting with the relative pronouns who, that, which, whose, where, when. They are most often used to define or identify the noun that precedes them. (source)

There is nothing incorrect in answer A.

Both B and C are theoretically possible, but sound a little awkward.

B basically says the same thing as the original phrase, and it is sort of a dogm (which I personally often ignore) that a separate sentence is better than attaching it to a previous one as a coordinate clause, with a semicolon between. The choice between two sentences and a compound sentence would be determined by the general flow of the surrounding text (the whole paragraph in which these sentences would appear). We don't have context here, so a dogm would win. It is at the very least not an improvement over the original phrase.

C again creates a situation where it is stylistically better to separate things into two different sentences. It is again rather a deterioration than an improvement over the original phrase.

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