The correct option is C laugh
The given sentence is a Type 1 conditional, because it presents a possible condition (if-clause) and its probable result.
In
such sentences, the if-clause is in simple present tense and the main
clause is in the simple future tense ('he will feel bad').
Option C: 'Laugh' is in the simple present
tense. It completes the sentence in meaning as well as agrees with the
Type 1 structure. Hence option C is correct.
Option A: 'Will laugh' is in the future tense, whereas the tense required is simple present.
Option B: 'Wouldn't laughed' is grammatically incorrect. The modal 'wouldn't' is to be followed by the verb 'laugh', as 'would' expresses a condition and does not express the past tense (laughed).
Option D: 'Would laugh' expresses a condition in the past tense, and is used in the mixed conditional type (an unreal past condition and its probable result in the present). Also, the if-clause won't contain the conditional verb 'would'.
Hence, options A, B and D are incorrect.