If nominal GDP increases by 10 percent from one year to the next but real GDP is unchanged, then:

1. A) Factor costs have increased by 10 percent but net indirect tax rates have not changed.
2. B) Factor costs have not changed but net indirect tax rates have increased by 10 percent.
3. C) The GDP deflator has increased by 10 percent.
4. D) All the above.

Apparently the answer is option D but how come? could you explain it please?