珠穆朗玛峰上生物稀少，在那里生物的生存主要受到哪些因素的制约 [ ]
A．温度
B．水
C．营养物质
D．阳光
答案：A
磁粉有多种颜色是因为与（）形成对比，使显示容易看到。
Wei Zhang has funds on deposit with Iron Range bank. The funds are currently earning 6% interest. If he withdraws $15000 to purchase an automobile, the 6% interest rate can be best thought of as a(n) :（）
A. discount rate.
B. required rate of return.
C. opportunity cost.
