the past year as an exchange student in Hong Kong, Linda appears more mature than those of her age.

A．Spending

B．Spent

C．Having spent

D．To spend

预聚系统热媒系统使用过程中最常见的故障是（）。

A、管线泄漏

B、热媒泵故障

C、泵入口阀内漏

D、泵出口阀内漏