Hello from MrBillDoesMath! 
 
Answer: 
 Choice D, x-2
Discussion: 
 Observe the the highest order term in the numerator is x^4 and the highest order term in the denominator is x^3. So the highest order term in their quotient is x^4/x^3 = x. Choice D is the only possible answer as all other choices start with x^2
 
Regards, 
 
MrB