单选题
In a certain formula, p is directly proportional to s and inversely proportional to r. If p=1 when r=-0.5 and s=2，what is the value of p in terms of r and s?
【正确答案】
C
【答案解析】[解析] 根据题意p可表示为：[*]
再把r=0.5，s=2和p=1代入上式可得
[*]
再把r=0.5，s=2和p=1代入上式可得
[*]