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.

Photons have no mass and ____ electrical charge.
no

Many people have ____ symptoms until they suffer chest pains or a heart attack.
no

Gerbils get reproductive when they reach sexual maturity at the age of ____ months.

three