Dna replication always proceeds in only one direction because the of the incoming nucleotide is attached to the free of the growing dna strand.

This question had a list of choices. The choices were:

A) 5'-phosphate / 3'-hydroxyl
B) 3'-phosphate / 5'-hydroxyl
C) 5'-deoxyribose / 3'-base
D) 3'-base / 5'-deoxyribose

Dna replication always proceeds in only one direction because the 5'- PHOSPATE of the incoming nucleotide is attached to the free 3'-HYDROXYL of the growing dna strand.

Choice. A. 

When you are making a guess you are forming a hypothesis