The correct option is C Many were there but I did not know anyone.
The basic order of words in a simple sentence is: subject (S) + verb (V) + object (O).
A sentence may not contain an object, depending on the verb. Transitive verbs like 'appear', 'die', etc do not require objects.
To
this basic structure, different elements can be added. For example,
noun phrases, adjective phrases, subject complements, types of clauses
and so on.
A compound sentence is made of two clauses, each having its own SVO form. Hence the basic structure of such a sentence is: SVO + conjunction + SVO.
Option C: The structure in this sentence complies with the basic structure:
S (Many) + V (were) + adverb (there) + conjunction (but) + S (I) + V(did not know) + object (anyone)
Hence C is correct.
Option A: The sentence formed isn't quite meaningful. It is correct grammatically, but the conjunction 'but' does not form the required contrast.
Options B and D: In both these options, the order is a jumble of words which do not form a coherent meaning.
Hence options A, B and D are incorrect.