《三国演义》中,张颌的死因是什么?
参考答案:中箭而死。
Scientists are convinced ____ the positive effect of laughter ____ physical and mental health. [ ]
A. of;at
B. by;in
C. of;on
D. on;at
为什么大、中跨桥梁的两端要设置桥头引道?