It means that the cell must only let in certain items and must only allow a certain amount of something into the cell
CFCs are Chlorofluorocarbon substances used in refrigerants (subtances used to keep other things cold) and in aerosol products.
they are both relatively nontoxic(nonpoisonous) and nonflammabale - at least as compared to alternatives.
They are rather volatile - they are not very stable. Therefore it does not make sense to say that they are strong - the correct answer is then strength.
Answer:
Cellulose is a polysaccharide composed of a linear chain of β-1,4 linked d-glucose units with a degree of polymerization ranged from several hundreds to over ten thousands, which is the most abundant organic polymer on the earth.