命题“圆的直径所对的圆周角是直角”是______命题.(填“真”或“假”)
在同圆或等圆中,同弧所对的圆周角是圆心角的一半,因此,直径所对的圆周角是直角.
∴是真命题.
Every minute is made full use of __ at our lessons.
A.to work
B.working
C.having worked
D.being worked
国际贸易惯例虽不具有法律的普遍约束力,但是如果当事人在合同中采用了某项惯例,则它对合同双方当事人就具有约束力。( )