What day _____ it the day before yesterday? [ ]

A. am

B. is

C. were

D. was

制冷系统出现高压报警，可能是由（）。

A.氟里昂注入量偏少

B.室外冷凝器翅片脏堵

C.系统内有堵塞引起局部节流

D.蒸发器风机风量偏小