The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion.
Life span of organisms are not necessarily correlated with their sizes. For example, the size of crow and parrot are not very different yet their life spans show a wide difference. Lifespan of a parrot is 140 years and that of a crow is 15 years. Similarly, a mango tree has a much shorter life span as compared to a Peepal tree.