D.
A is wrong because if they were proportional, they'd both be 1/2 since their denominators did not change.
B is wrong because if you were to change 2/1 to a fraction with a demoninator with an 8, it'd be 16/8.
C is wrong because if you were to change 1/2 to a fraction with a denominator with a 4, it'd be 2/4.
D is right because they changed 2/1's denominator to 8. If 1 changed to 8, that means the fraction got multiplied by 8. The fraction should be 16/8 which it is, so D is right
