Physics - NLM Question with Solution | TestHub

Newton's third law pairs act on two different bodies and are of the same nature.

(C) Earth pulls the block (gravity on the block) and the block pulls the earth (gravity on the earth) - a third-law pair. Correct.

(D) The block pulls the string and the string pulls the block - action-reaction at the contact. Correct.

(A) Both forces are exerted by the string on two different bodies; they are not action-reaction. (B) The two forces act on the same body (the block); they cannot be a third-law pair.

Hence (C) and (D).