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.

Fire occurs any time ____ elements are present - fuel, heat, oxygen and the chemical chain reaction.
four

Titanium is found in column ____ along with chemically similar zirconium, hafnium, and thorium.
four

Mollusks have one or ____ hearts.

two