Which one(s) is/are correct about porins?

I.    They are proteins.

II.   They form large pores in the inner membrane of plastids, mitochondria and some bacteria.

Ill.  They allow molecules up to the size of small proteins to pass through.

• A

  All are correct

• B

  All are incorrect 

• C

  I and Ill are correct

• D

  I and II are correct