Imperceptible to the eye or the ear, carbon monoxide is formed from materials containing carbon, or carbonaceous materials, are only partially combusted.
A. carbon monoxide is formed from
Imperceptible to the eye or the ear, is a modifier that modifies carbon monoxide.
The non underlined part says
materials containing carbon, or carbonaceous materials, are only partially combusted.
Are only partially combusted talks about carbonaceous materials,
If we remove the modifier the sentence would read
Carbon monoxide is formed from carbonaceous materials, are only partially combusted.
The first clause- Carbon monoxide is formed from carbonaceous materials- has a subject (Carbon monoxide) and a verb (is formed)
What is the subject of the verb (are only partially combusted)
in the next part of the sentence? Carbon monoxide or carbonaceous materials
The sentence construction is wrong. Eliminate
(B) carbon monoxide is formed by
Same as A. Eliminate.
(C) the formation of carbon monoxide is when
What is- Imperceptible to the eye or the ear? Formation of carbon monoxide or carbon monoxide? It is the latter and hence must be placed next to the modifier. Eliminate
(D) carbon monoxide is formed when
Now, the sentence would read
Carbon monoxide is formed when carbonaceous materials, are only partially combusted.
By adding “when”
Carbon monoxide is formed when carbonaceous materials, are only partially combusted.
The subject of the verb- are only partially combusted in the second clause is carbonaceous materials
Correct.
(E) carbon monoxide forms when its
Carbon monoxide forms when its carbonaceous materials, are only partially combusted.
The passive voice- “is formed” is preferred in this sentence. Eliminate