Derrick and melissa had been practicing for the last two weeks, but she still felt like they weren't ready. their recital was on the 15th. they had both played in the school's band for the last two years. melissa was a more experienced player.

the days flew by. the worry never disappeared. it was the night before the recital. melissa paced back and forth. it was her bedtime. she wasn't ready to sleep. all of the notes seemed to drift from her head like steam from a smokestack. she wondered if derrick was as nervous. she thought about the crowd, and it made things worse.

1. the days flew by. the worry never disappeared.

without changing the meaning, what is the best way to change these simple sentences into one compound sentence?
as the days flew by but the worry never disappeared.
the days flew by and the worry never disappeared.
the days flew by, but the worry never disappeared.
the days flew by but the worry never disappeared.