求：Demand in 和 Demand for 区别及用法

Because of less availability and greater demand for scientific research, platinum remains consistently expensive, like gold.

a) Because of less availability and greater demand for scientific research, platinum remains consistently expensive, like gold.
b) Because of less availability and increased demand for scientific research, platinum remains consistently expensive, like that of gold.
c) Because of decreased availability and increased demand in scientific research, platinum remains expensive, like gold.
d) Because of decreased availability and increased demand for scientific research, platinum remains expensive, like gold.
e) Because of decreased availability and greater demand in scientific research, platinum remains at a consistently high price, like that of gold.

正确选项是 C
哪位高人指点一下小女不知这 demand in 和 demand for 神马时候用哪一个啊？