人们在切西瓜时，流出的汁液来自细胞的[ ]
A．细胞膜
B．细胞质
C．液泡
D．细胞核
C
工业上实现热量交换的设备统称为（）。
They asked me____________ during the May Day holidays.[ ]
A. where had I gone
B. where I had been
C. where had I been
D. where I had gone
