Question

1. what structural feature of the cell membrane allows it to be selectively permeable?

a. the presence of channels and pores.
b. the double helix structure of dna.
c. its rigid outer layer
d. the fluid inside the nucleus.

Explanation:

The cell membrane's selective permeability is due to its structure. Channels and pores (like transport proteins) control what enters and exits. DNA's double - helix (b) is for genetic info storage. A rigid outer layer (c) (like in plant cell walls) is not about permeability selection. The fluid inside the nucleus (d) is nucleoplasm and not related to cell membrane permeability.

Answer:

a. The presence of channels and pores.