His grandfather keeps exercising all year around, even in the hottest days in summer and the coldest days in winter.

A、他爷爷常年坚持锻炼，冬练三九，夏练三伏。

B、他爷爷除了最炎热的夏天和最寒冷的冬天全年都会坚持锻炼。

C、他爷爷在最炎热的夏天和最寒冷的冬天坚持锻炼。