-个练习本的单价是a元，买b本，应付______元．
a×b=ab（元）；
故答案为：ab．
下列哪项不是运动系统的组成部分[ ]
A．骨
B．关节
C．肌肉
D．胃
After the 5-hour long journey, all the tourists were_____and desperate to have a good rest．
A．turned out
B．given out
C．run out
D．burnt out
