___________A] when [B] since [C] for [D] whereas

He cannot be tired _______ he has walked only half a mile. A：since B：whether C：when

Hard______they tried, they failed to climb to the mountain topA．ifB．when.C．asD．since

___________[A] when [B] once [C] while [D] whereas

_________(57)A.like B.as C.for D.since

_________(62)A.for B.asC.because D.whereas

_________(53)A.since B.whereC.though D.when