In which animals are the blood and the interstitial fluid considered to be the same body fluid?

In insects such as cockroach, grasshopper

Explanation:

Insects such as grasshopper has open circulatory, in them the body fluid is the hemolymph. The hemolymph does contain any respiratory pigment. It bathes the organs directly as it is pumped between open spaces in the body.

Thus, in insects, the blood and the interstitial fluid considered to be the same body fluid?

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."