The prepositional phrase for this sentence is "go until Friday." The word "go" is a preposition. Think of it as a squirrel and a log. To find a preposition, say "The squirrel (went) [insert preposition] the log." If it makes sense, it is a preposition. Then just find the phrase to go along with it!
B. Is the answer I just did and I got right
Sam and Eric are twins. Though they are two individuals, they are identified as one with the nickname "Samneric".
Their companions can't tell them apart so instead of using their names, their friends combined their names and used it to address any one of the twins.
Samneric do things together. They think alike. Basically, they are identical in all ways from physical appearance to their characters.