患者，男性，43岁，因风湿性心脏病二尖瓣狭窄并关闭不全、心房颤动、心功能不全，长期服用地高辛0.25mg/d及培哚普利、氢氯噻嗪、螺内酯等治疗。5天因恶心、呕吐、腹泻、腹痛，拟“急性肠炎”自行口服“黄连素”，症状好转。现感上腹部不适，食欲下降，乏力、心悸、头昏，心电图检查示：多源室性期前收缩。患者病情变化的原因应首先考虑的是（）

A.心力衰竭加重

B.电解质紊乱

C.慢性胃炎

D.培哚普利致直立性低血压

E.洋地黄过量

It was with great joy _______ he worked out the problem that he had long been puzzled about.

A．which

B．that

C．because

D．since