Mr. Smith couldn’t open the door because his naughty boy ______ it from the inside.

A．would lock

B．was locking

C．has locked

D．had locked

矩形的周长为50，设它的长为x，宽为y，则y与x的函数关系为[ ]

A．y=﹣x+25

B．y=x+25

C．y=﹣x+50

D．y=x+50