Correct Option : C
[Although, Eventhough, Inspite, Despite, However, But] - are some commonly used words, which are used to describe contrast meaning in the sentence, let me put some examples for better understanding, mentioned below, the meaning of all sentence is same, only difference is the grammertically usage.
Although we don't agree, I think she's a brilliant speaker.
Even though we don't agree, I think she's a brilliant speaker.
In spite of the law, people continue to use mobile phones while driving.
Despite the law, people continue to use mobile phones while driving.
in spite of / despite : After in spite of and despite, we use a noun, gerund (-ing form of a verb) or a pronoun.
although / even though : After although and even though, we use a subject and a verb. Even though is slightly stronger and more emphatic than although.
Though:Though can be used in the same way as although. Though can also go at the end of the second phrase.
But is a Conjuction, majorly used between the sentence of two contrast clause.
with this knowledge, we are able to eliminate A, and D. Remaining with B, C and E
(B) but it may be temporary only - Worng, due to Pronoun
"it" - usage creates ambiguity
(C) but the drop may be only temporary -
Correct(E) but such a drop may only be a temporary one - usage of "Such" determiner to modify Drop, and "be a temporary one" wordy phrase, is not required to simple meaning indicated by D -
makes E eliminate