(2)20- 14=6 (person),
There are six more people who like to drink milk than those who like to drink soda.
(3) 20+14+18+14 = 66 (person),
There are 66 students in Class One.
According to the survey results, we should buy more milk for the next party in this class.
So the answer is: milk, 6, 66, milk.