Option C: “I’ll” is the shortened form of “I will”. With it the sentence would become, “I will wait for the passengers to board.”, which is a meaningful sentence. Hence, this is the correct option.
Option A: “Aisle” refers to the space between two rows of seat. This is meaningless in the given case. Hence, this option is incorrect.
Option B: “Isle” refers to an island. This is meaningless in the given case. Hence, this option is incorrect.
Option D: “Ale” is a form of beverage. This is meaningless in the given case. Hence, this option is incorrect.