Eric made a physical model of a cell membrane by putting one zip-top plastic bag inside another. He punched some straws through the plastic so that they led from outside the outer bag to the inside of the inner bag.

Which of the following features of a cell membrane can be seen using Eric's physical model?

Proteins and other molecules can move around within the cell membrane.
A cell membrane is made of two layers.
Some molecules can pass directly through the cell membrane.
Pores and proteins in the cell membrane allow passage through it.