The following sentence has been split into four segments. Identify the segment that contains a grammatical error.
“Do you want to join us for lunch?” / “I’m sorry my physics class/ will start at 1 p.m. and doesn't/ finish till 3 p.m.”

Correct option is A

The segment (a) contains a grammatical error. Considering the regularity of action, the correct form should be "starts at 1 p.m. and doesn’t"
This implies that the physics class starts at 1 p.m. regularly or as a scheduled routine.
The correct sentence should be: "Do you want to join us for lunch?” “I’m sorry, my physics class starts at 1 p.m. and doesn't finish till 3 p.m."
This maintains the present simple tense, which is used for habitual actions and regular schedules.