题干
There are many cars coming up and down. If you insist on standing there, you will risk _________ down on the ground.
A：knocking
B：to knock
C：being knocked
D：knocked
答案(点此获取答案解析）
C
为虚数单位，
为实数，则“
”是“复数
在复平面上对应的点在第一象限”的