Arrange the following five events in an order that explains the mass flow of materials in the phloem.

1. water diffuses into the sieve tubes.
2. leaf cells produce sugar by photosynthesis.
3. solutes are actively transported into sieve tubes.
4. sugar is transported from cell to cell in the leaf.
5. sugar moves down the stem.

a) 2, 1, 4, 3, 5
b) 1, 2, 3, 4, 5
c) 2, 4, 3, 1, 5
d) 4, 2, 1, 3, 5
e) 2, 4, 1, 3, 5