請問whether 和 if 的差別

請問各位nn...

whether 和 if 的差別在哪裡

我寫題目時雖然靠感覺選出了正確答案

但是我說不出正確答案哪裡好,錯的答案哪裡不好~~

我做的題目如下不是987裡的)

In recent months, there has been considerable debate over if increased taxes should

be a first or last resort in balancing the budget.

a.over if increased taxes should be a first or last resort in balancing the budget.

b.over whether increased taxes should be a first or last resort.

c.about increasing taxes being first or last resorts

d.about if increased taxes is a first or last resort

e.concerning tax increases and their being first or last resorts

正確答案:b

請各位nn幫幫忙,謝謝了~

引导名词从句多不用if, 而用whether