张某，男，57岁。2天前曾感心悸，心烦，周身乏力，胸闷不舒等症状。今晨起上腹部剧疼，

We don't go to school _____ Saturdays or Sundays. [ ]

A. at

B. for

C. on

It was foolish of him to ________ his notes while taking such an easy test, and as a result, he got punished.

A．refer to

B．speak of

C．cheat in

D．take out

眼底的改变可以反映高血压的严重程度。按照“Keith-Wagener”眼底分级法，眼底改变Ⅲ级是指（）

A.视网膜动脉狭窄

B.视神经 * * 水肿

C.视网膜动脉变细

D.眼底出血或渗出

E.动脉交叉压迫

在直接标价法下，较低的价格为外汇卖出价，较高的价格为外汇买入价。

两台离心泵并联，当它们单独工作时，每台离心泵流量为100m/h，当它们并联工作3时，每台泵单独流量为80m/h，问当并联工作时，它们总排量为多少？已知：Q单=100m/h，Q1=Q2=80m/h求：Q总=？