请简述目前常见的供暖系统定压方式？
参考答案：1、高位膨胀水箱定压
2、电接点压力表补水泵定压
3、膨胀稳压罐气体定压
4、变频补水泵定压
____ in the countryside, though living in town, he ___ his home village all the time.
A．Brought up; has still thought of
B．Being brought up; is still thinking of
C．Having been brought up; still thinks of
D．Brought up; is still thinking of
联锁系统除应进行分项试验外，还应进行（）试验。
A、回路
B、系统
C、整套联运
D、A、B、C
ought of