Giant kelp has gas-filled sacs to it float so it can

a. collect more sunlight

b. trap small fish

c. move with the ocean waves

d. send signals to other plants

The answer to this question would be: A.Collect more sunlight

Giant kelp using the air inside it sac to push its body so it would float in the ocean. This will make it able to take more sunlight since sunlight intensity will be lesser in the deeper area of the sea. More exposure to sunlight will increase the photosynthesis rate of the giant kelp so it can produce more food.