During the scientific experiment, Mr. Chen carefully poured the water into the tube, with my classmates ____ beside to see what would happen.

A．were standing

B．stood

C．standing

D．to stand

哪些部位受刺激可产生尿路刺激征（）

A.膀胱三角区和膀胱颈

B.输尿管

C. * *

D.膀胱前壁和膀胱颈

E.膀胱后壁和膀胱颈