If a and b are both factors of 50, which of the following must be true

We are informed that a and b are factors of 50. We are to determine which of the answer choices must be true.
factors of 50 are {1,2,5,10,25,50}.
In A, we are given that ab≥2. This is not always true for the situation a=b=1, where ab=1.
In B, a+b≤50. This also not always true for the situation a=25, and b=50, whereby a+b=75.
In C, ab is factor of 100. This not always true for a=10 and b=25, where ab=250.
In E, ab is even. This is not necessary true for a=1, and b=5, where ab=5, which is not even.
In D, ab is a factor of 2500. This always true since taking the highest possible values that a and be can take, a=b=50, and computing ab=2500. In this case 2500 is a factor of 2500. Hence D must be true.

Answer is therefore D.