27. If vesicles are almost constantly pinching off from the ER to carry proteins to the Golgi apparatus,
why does the ER not shrink and finally disappear?

The ER WILL disappear but that happens when it is compromised or the cell dies. The ER or Endoplasmic Reticulum are set in 2 group Rough ER and ER those are not related to the subject. The ER shrinking is likely a cause of mutation and the cell will eventually die, otherwise the ER should not shrink and disappear.

i believe it's c. the trait for large beaks will be passed on to future generations through natural selection.

since eventually smaller beaks would have to find another source of food or even eventually just die out from the lack of food.