Mr Smith has a limited income which restricts the number of different goods he can buy. Which one of the following best describes the position at which Mr Smith's utility from purchasing different goods is maximised?
选项：

A:Marginal utility from each good is equal;
B:Ratio of marginal utility to price is equal for each good;
C:Marginal utility from each good is 0;
D:Total utility from each good is equal