The slow block to polyspermy is due toa) a transient voltage change across the membrane.b) the consumption of yolk protein.c) the jelly coat blocking sperm penetration.d) formation of the fertilization envelope

The slow block to polyspermy is due to d) formation of the fertilization envelope.

Here's a step-by-step explanation:

1. When a sperm first fuses with an egg, it triggers a fast block to polyspermy which is a transient voltage change across the membrane. This prevents other sperms from fusing with the egg.

2. However, this fast block is temporary and lasts only for a few seconds to a minute. Therefore, a slow block is needed to ensure that no other sperm can fertilize the egg.

3. The slow block to polyspermy involves a series of biochemical events that lead to the formation of the fertilization envelope.

4. The cortical granules in the egg's cytoplasm release their contents into the perivitelline space (the space between the plasma membrane and the vitelline envelope of the egg).

5. This causes the vitelline envelope to lift away from the egg and harden, becoming the fertilization envelope.

6. The fertilization envelope is impenetrable to other sperms, thus preventing polyspermy.

So, the answer is d) formation of the fertilization envelope.