Excerpt from The Coded Letters
Lee Washington

7 “These games were incredibly suspenseful, but we were never envious if the other person won the game,” Grandma explained. "I started our first game by writing the first letter. In it, I wrote the code to describe my first move. In all my subsequent letters, I made moves based on my opponent's moves."

The words subsequent and submerge both contain the prefix sub. Based on this information, what does the prefix sub MOST LIKELY mean?

A)
under or secondary

B)
true or verifiable

C)
tricky or difficult

D)
around or centered on