66. There are six boxes of oranges, apples, and pears. The weights of these six boxes of fruit (unit: kilograms) are: 15, 16, 18, 19, 20, 31. The weight of the apples is half that of the pears, and there is only one box of oranges. The 15-kilogram box contains $\qquad$, the 19-kilogram box contains $\qquad$, the 20-kilogram box contains $\qquad$, and the 31-kilogram box contains $\qquad$. (Fill in the four blanks with the sequence numbers before the following fruit varieties).
1. Oranges 2. Apples 3. Pears