Answer: They are sterile
Explanation:
Mule is a hybrid of male donkey and female horse with different chromosome number and is considered superior to both horse and donkey. Still it is considered as a weak hybrid this is because the mule is sterile which means that it cannot reproduce further.
The mule though is superior in many ways such as it can jump and is strong. The hybrid of mule is not good as it cannot continue its next generations on earth.
They are sterile and so is a weak hybrid.
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The breathing process occurs as follows: Inhalation increases the volume of the lungs, which reduces internal pressure and causes air to enter. Then the exhalation makes the opposite process. Gaseous exchanges occur in the lung alveoli and are responsible for eliminating the gases we do not need and preparing the oxygen to be spread throughout the body.
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