Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Sentence1: when a hemisphere is tilted away from the sun , that hemisphere receives less direct sunlight. 
Sentence2: Sunlight is delivered in small packets of energy called photons.
sunlight

Sentence1: melting is when solids are heated above their melting point. 
Sentence2: Ice is a solid, it's cold and it's hard.
solids

Sentence1: RNA is ribonucleic acid Like DNA, it is a nucleic acid. 
Sentence2: ribonucleic acid is a small molecule that can squeeze through pores in the nuclear membrane.

acid