If there are only two goods,an increase in the price of good1 will increase the demand for good2:
(A)if and only if price elasticity of demand for good2 is greater than 1 in absolute value
(B)whenever both goods are normal goods
(C)only if the two goods are perfect substitutes
(D)never
(E)none of the above
答案是A，但是我不知道这怎么判断出来的，求大家指点啊！！