Final answer:
The poly A tail protects mRNA from degradation in the cytosol.
Step-by-step explanation:
The correct answer is C) poly A tail.
Before the mRNA leaves the nucleus, it is given two protective 'caps' - a 5' cap and a poly-A tail. The 5' cap is composed of a methylated guanosine triphosphate molecule (GTP) that is placed at the 5' end of the mRNA. The poly-A tail is a long chain of adenine nucleotides attached to the 3' end of the mRNA. These protective caps prevent the ends of the mRNA from degrading during its journey in the cytosol.