(5) The largest number of trees are planted;

(2)(25+20+30+25)÷4

= 100÷4

=25 (tree)

A: On average, 25 trees are planted in each class;

(3) How many trees were planted in Class Five (2) than in Class Five (1)?

25-20=5 (tree)

Answer: Class 5 (2) planted 5 fewer trees than Class 5 (1).