问题：

[单选题]When does the actual calculation happen?什么时候进行实际的运算？Unt答案窝(daanwo.com)-大学作业答案分享平台
AEach time a new number is encountered每遇到一个新的操作数Unt答案窝(daanwo.com)-大学作业答案分享平台
BEach encounters a new operator每遇到一个新的操作符Unt答案窝(daanwo.com)-大学作业答案分享平台
CThe current operator has a higher priority than the operator on the top of the stack当前的操作符比栈顶的操作符优先级高Unt答案窝(daanwo.com)-大学作业答案分享平台
DThe current operator has a lower priority than the operator on the top of the stack当前的操作符比栈顶的操作符优先级低