Three sentences are given. You need to find if they are grammatically correct or incorrect and mark the answer accordingly.

(P) The two boys were startled at the fresh muddy imprints of a pair of bare feet.

(Q) Further footprints followed one after other, descending the steps and progressing down the street.

(R) The boys followed, fascinated, until the muddy impressions became fainter and fainter, and at last disappeared altogether.