Nutrients enter a cell the concentration gradient by the process of

Nutrients enter a cell up the concentration gradient by the process of active transport.

Nutrients enter a cell with the concentration gradient by the process of diffusion.

The answer is b, as with an inference you make a statement with no evidence

Although i don't know what is the simulated system, starfish are predators that eat mostly  microalgae,  snails, sponges, bivalves, mussels and other small marine animals. removing starfish from any system would definitely increase this animals that they prey.