Question

the plane took off before all passengers boarded​

Answer 1

Answer:

After

Explanation:

The plane took off after all passengers boarded.

Answer 2

Answer:

There are any number of reasons you might be called by the gate agent before or during boarding: You requested an upgrade and the agent determines they can honor your request (a seat is unsold, someone has changed plans and opened up a seat, someone is likely to mis-connect and you get their seat).