下列食用菌在分类上位于子囊菌门的是（）。
A、松茸
B、美味牛肝菌
C、蛹虫草
D、鸡腿蘑
参考答案：C
He had the horse _____ all the way. As a result, he fell off the horse and had his arm _____. [ ]
A. running; break
B. running; broken
C. run; breaking
D. run; broken
粉笔盒重10N，黑板擦重5N，现将黑板擦放在粉笔盒上再一起放在讲桌上，这时桌子受到的压力大小为 [ ]
A．10N
B．5N
C．15N
D．20N
