锅炉的三大安全附件是什么？
参考答案：
安全阀、压力表和水位表。
— I have got a headache.
— No wonder. You _____ in front of that computer too long.[ ]
A. work
B. are working
C. have been working
D. worked
伸大腿、屈膝的肌是（）
A.股薄肌
B.长收肌
C.短收肌
D.大收肌
E.股二头肌
