Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

Question: As a polycrystalline material solidifies, grains with irregular shapes form. the interfaces between grains constitute grain what? Answer: boundaries
Grain boundaries. As a polycrystalline material solidifies, grains with irregular shapes form. The interfaces between grains constitute grain boundaries. (Squares represent unit cells within grains.

Question: The voltage of a voltaic cell can be determined by the reduction potentials of what? Answer: half reactions
The voltage of a voltaic cell can be determined by the reduction potentials of the half reactions.

Question: By what are skeletal muscles attached to bones? Answer: tendons
Most muscles are skeletal muscles, which are attached to bones by tendons. Skeletal muscles work in pairs to move bones back and forth at joints.