若幂函数y=xa2-4a-9为偶函数，则a的值不可能是（　　）

A．5

B．4

C．3

D．1

The nurse is teaching the client how to use a cane. Which of the following statements is most inaccurate

A．The client should hold the cane on the involved side.

B．The client should hold the cane close to his body.

C．The stride length and the timing of each step should be equal.

D．The nurse should stand behind the client to prevent falls.