* SC: from vs when

[Nishant.Chandra]

Visible as smog, ozone is formed in the atmosphere from X and Y.

(A) ozone is formed in the atmosphere from
(B) ozone is formed in the atmosphere, and when
(C) ozone is formed in the atmosphere when
(D) ozone, formed in the atmosphere when
(E) ozone, formed in the atmosphere from

Correct answer is C.

It is obvious that D and E are incorrect because they create sentence fragment.

Can someone kindly enlighten me about the correct use of "from" and "when". I ommited C, D, E because I am under the impression that "when" is used for references in time. This sentence does not make any reference in time thus I went with A.

Therefore, can someone summarize the context in which we use the following-- 'when' and 'from'

I shall be greatful to you.

Source: own construction!!!

[JonathanSchneider]

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