I believe the correct answer is B. Nephridia are excretory organs. They are organs found in invertebrate animals that are present in pairs and are responsible for performing functions that are similar to the kidney of a vertebrate. They excrete wastes from metabolic processes.
An exponential growth graph looks pretty much like the right side of a parabola. The graph equation is f(x)= C ·a^x, so you can also plug in x values to find the y value. It's not a linear line, but it curves upwards starting from (0,0).
Answer:
oxygen enters blood cells by 'diffusion'