问题：
We rushed to the football court, only to see a sign _____ into the ground reading PERIODIC MAINTENANCE (定期维修).
A．knocked
B．knocking
C．to be knocked
D．being knocked
We rushed to the football court, only to see a sign _____ into the ground reading PERIODIC MAINTENANCE (定期维修).
| A．knocked | B．knocking | C．to be knocked | D．being knocked |
参考答案：