A client who is 7 months pregnant reports severe leg cramps at night. Which nursing action would be most effective in helping her cope with these cramps（）

A. Suggesting that she walk for 1 hour twice per day.

B. Advising her to take over-the-counter calcium supplements twice per day.

C. Teaching her to dorsiflex her foot during the cramp.

D. Instructing her to increase milk and cheese intake to 8 to 10 servings per day.

物体做平抛运动的轨迹如图所示，O为抛出点，物体经过点P（x₁，y₂）时的速度方向与水平方向的夹角为θ，则

A．tanθ＝y₁/2x₁

B．tanθ＝2y₁/x₁

C．物体抛出时的速度为v₀＝x₁

D．物体经过P点时的速度v_p＝