Biology

The correct answer is: A.Allows some, but not all molecules to cross.

"Selectively permeable" refers to a property of cell membranes that allows them to control which molecules can enter or leave the cell. It means the membrane permits certain substances (such as small molecules or specific ions) to pass through while restricting others. This is typically achieved through the use of specialized channels, transporters, or carriers in the membrane.

Here's a brief breakdown of the other options:

B.Allows all molecules to cross but still regulates how much goes through: This isn't correct because selectively permeable membranes don't allow all molecules to cross, but rather they are selective about which ones can pass.