This is true. when it is warmer the planet and insects can migrate to thses other places so they do not have to die or hibernate through winter.
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The correct answer is (a.) Its spindle-shaped cells allow it to do smooth muscles. The structure of the cardiac muscles which is spindle-shaped is very important for the heart to withstand the stretching of the muscles during the contractions. Also for its smooth surface which is very important to prevent any possible blood clot during circulation.