电力系统的备用接线方式包括()。
参考答案:双回路放射式,干线式,链式环式两端供电网
(2013·西安一中月考)As ________ unemployment is very high at the moment,it's very difficult for people to find ________ work.
A.the;/
B./;/
C.the;a
D.an;the
对突出的孔洞怎样处理?