TASK DEFINITION: Given a sentence, fill out the missing word with a 'no' or a number (between zero and ten). You should write the numbers with english alphabet, like: four instead of 4.
PROBLEM: Photons have momentum but ____ mass or electrical charge.

SOLUTION: no

PROBLEM: Narwhals have ____ teeth in their upper jaw.

SOLUTION: two

PROBLEM: Light chains exist in ____ classes, lambda and kappa.

SOLUTION:
two