Which of the following will occur in an IS-LM model, if the government decides to raise the income tax rate?
选项：

A:the IS-curve will become flatter and shift to the right
B:the IS-curve will become steeper and shift to the left
C:the IS-curve will shift parallel to the left
D:the LM-curve will become steeper and shift to the right
E:the LM-curve will shift parallel to the right