可靠性优化规划指当确定在何时、何地投建何种类型的电力设备,以到达规划周期内所需要的电力供给能力,在满足电力系统可靠性等技术指标的前提下使电力系统的()。
参考答案:总费用最小
网络图中,中间节点()。
A.既无外向箭头,也无内向箭头
B.只有外向箭头
C.既有外向箭头,也有内向箭头
D.只有内向箭头
Since the global financial crises , the export of Chinese goods has managed to ____ roughly, and now everything goes well in foreign trade.
A.close up
B.keep up
C.add up
D.hold up