“每一只蝴蝶在破茧之前都有一段极其痛苦的经历，也正是那痛苦装点了它的美丽。”对这句话理解正确的是[     ]

A．所有美丽的动物都有一段极其痛苦的经历

B．挫折孕育着成功，挫折是走向成功的必经之路

C．有些人可以不经历挫折就获得成功

D．人只有经历挫折才会美丽迷人

David and Susan didn’t give in to each other, so they _________ the whole time they were together.

A．have quarrelled

B．had quarrelled

C．were quarrelling

D．had been quarrelling