What do animals such as clams and oysters extract from the water to build their shells? A) fructose
B) silicon
C) hydrogen
D) carbon

I believe the answer is D) Carbon!

They also use calcium!

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.

it's anything that aren't producers and consumers.

explanation:

you've got to be clear on what "this" is