Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
:)
Answer:
why an athlete would need to be concerned about twitches or contractions is because, whenever they perform, and such thing happens, it will most likely distract the athlete, and cause the athlete doing his/her performance to not be as good, and may lead to failure, for example, when someone is running very fast for a sprinting race, and he has a contraction in his leg it will cause him to react by showing signs of pain by slowing down or even tripping and falling, causing him to lose the race.
Hope this Helped!
Cardiac Muscle Tissue<span>. Cardiac </span>muscle tissue<span> is an extremely specialized form of </span>muscle tissue<span> that has evolved to pump blood throughout the body. In fact, cardiac </span>muscle<span> is only found in the</span>heart<span> and makes </span>up<span> the bulk of the </span>heart's<span> mass.</span>
In this question, there are no options given to choose from. So i would answer this question based on my knowledge. The most likely cause of the observed variation is adaptation and evolution. The birds of that island adapted to the food source and then they evolved as per the requirement of the place and food source.
