'Binoculars' is a plural noun. The singular form is 'binocular', but it's never used in singular form. It's always referred to as a pair: a pair of binoculars, or just binoculars.
Option C: 'They' is a plural pronoun for binoculars. 'Are' is a plural verb that refers to them.
Since the noun (binoculars) is plural, the verb 'are' will also be plural. This is called subject-verb agreement.
Hence option C is correct.
Option A: 'It' and 'is' are both singular. They do not refer to the plural noun.
Option B: 'It' and 'was' are also singular. 'Was' is a past tense verb.
Option D: 'Were' is a past tense verb and the plural form of 'was'. It agrees in number to 'binoculars', but not in tense. The sentence is n the present time. 'I can't find' refers to 'now'. Hence the sentence is in present.
So, options A, B and D are wrong.