—The shoes are very nice. I'll take them.

—But you must _____ first. I think the size is a bit smaller for you.[ ]

A. pay for them    

B. try them on    

C. put them on        

D. take them off

层门机械联锁的作用是轿厢不停在该层层站处时，保证该层站外无法将此层门打开。