880. Two valence states of uranium, one with a deficit of four electrons and the other one with a deficit of six, occurs in nature and contributes to the diversity of uranium’s behavior.

(A) the other one with a deficit of six, occurs in nature and contributes
(B) the other one a deficit of six, occur in nature and contribute
(C) the other with a deficit of six, occurs in nature and contributes
(D) the other with a deficit of six, occur in nature and contribute
(E) one with six, occurs in nature and contributes

Solution:

Subject-verb agreement + Redundancy

In A, C, and E, subject-verb agreement is violated “two valence states (plural) ... occur (singular verb)...contributes (singular verb)” . Hence, these three choices are incorrect.
In B, “one” is redundant when used the second time- ”one ..... and the other one ....”. Hence, B is incorrect.
In D, “occur” and “contribute” (plural verbs) agree with “Two valence states”. Hence, D is the best choice.

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