What does Xiyangyang say to Labixiaoxin?

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A. Happy Birthday!                

B. Welcome to our school!

C. Happy Women’s Day!            

D. Merry Christmas!

平板闸门导轨安装中必须随时用（）进行校正，使其铅直无误。

A.直尺

B.仪器

C.垂球

D.皮尺