Which is true about the completely simplified difference of the polynomials a3b + 9a2b2 − 4ab5 and a3b − 3a2b2 + ab5?

The difference is a binomial with a degree of 5.
The difference is a binomial with a degree of 6.
The difference is a trinomial with a degree of 5.
The difference is a trinomial with a degree of 6.