题目

Think about vitamin D when you’re catching up on summer rays. It’s sometimes called the “sunshine vitamin” because it’s produced in your skin in response to sunlight. Vitamin D is a fat-soluble (脂溶性的) vitamin in a family of compounds that includes vitamins D-1, D-2, and D-3. It can affect as many as 2,000 genes in the body.  Vitamin D has several important functions. Perhaps the most vital are regulating the absorption of calcium and phosphorous（磷）, and promoting normal immune system function. Getting enough vitamin D is important for normal growth and developm1．做竖直上抛运动的物体，重力对物体做功的情况是（　　）A．下落过程做负功B．上升过程不做功C．上升过程做负功D．下落过程不做功