世界上第一张股指期货合约是由堪萨斯期货交易所开发的()。
A.道琼斯指数期货
B.标准普尔指数期货
C.上市价值线综合平均指数
D.主要市场指数期货
参考答案:C
Bricks covered the ground like red autumn leaves. No wind, _____, could blow them away. [ ]
A. but
B. besides
C. however
D. except
某膨胀机进口的比焓值为80J,出口实际比焓值为65J,理想情况下膨胀机出口的比焓60J,问膨胀机的效率为多少(按%即)?