The given sentence already contains a main verb 'want'. Thus, the answer must be a non-finite verb.
Option A is incorrect, 'uses' is a verb. Having two main verbs in one sentence will make it grammatically incorrect. Thus, it is not the correct answer.
Option B is incorrect, 'likes' is a verb. Having two main verbs in one sentence will make it grammatically incorrect. Thus, it is not the correct answer.
Option C is correct, 'to use' is a non-finite of the infinitive form. Thus, it shows that Peter has to use a pocket calculator now, without making the sentence incorrect. Thus, it is the correct answer.
Option D is incorrect, 'be' is a verb. Having two main verbs in one sentence will make it grammatically incorrect. Thus, it is not the correct answer.