Organize the following polynomial expressions from least to greatest based on their degree:
6x2
18x3 + 5ab − 6y
8a − 5
4x3y + 3x2 − xy − 4
III, I, IV, II
IV, II, I, III
III, I, II, IV
IV, I, II, III
6x2
18x3 + 5ab − 6y
8a − 5
4x3y + 3x2 − xy − 4
III, I, IV, II
IV, II, I, III
III, I, II, IV
IV, I, II, III