— When are you due to arrive?    

— ____.  [ ]

A. Yesterday                                  

B. In about two hours    

C. By bus                                    

D. With John

A ladder 25 feet long is leaning against a wall that is perpendicular to level ground. The bottom of the ladder is 7 feet from the base of the wall. If the top of the ladder slips down 4 feet, how many feet will the bottom of the ladder slip ？（）

A．4

B．5

C．8

D．9

E．15