Q: Fact 1: Plant reproduction often requires pollen. Fact 2: Bees feed on nectar and pollen. Given the two facts above, plant reproduction often requires nectar and what?

OPT:
[1]. earth.
[2]. food.
[3]. sun.
[4]. saliva.
[5]. seeds.
[6]. plants.
[7]. bees.
[8]. energy.
The answer is:
[7].