The external cell membrane. Even organisms as simple as bacteria have a cell membrane.
Prokaryotes do not have internal membranes but they still have external membranes.
Everything living thing has a cell membrane
You can use dimensional analysis to figure this out.
× 
= 3 grams
If done correctly, ml and ml will cancel out, leaving you with grams.
If you don't know dimensional analysis, simply multiply <em>3 ml</em> by <em>1 grams </em>and that should still get you 3 grams.
Answer: A) They are the site of protein synthesis.
Explanation:
Ribosomes are small round organelles attached to the endoplasmic reticulum in cells, and serve as site of protein synthesis. This is possible because the transfer RNA assembles amino acids to form polypeptide chains right in the ribosomes.
Thus, ribosomes are site of protein synthesis