Hxen.com's tips：Every day persisted can learn English well!-->■Learn English Everyday■
endangered - adj. used to describe a type of animal or plant that has become very rare and that could die out completely
pivotal - adj. very important
figure (something) out - phrasal verb. to understand or find (something, such as a reason or a solution) by thinking
mortality - n. the quality or state of being a person or thing that is alive and therefore certain to die : the quality or state of being mortal
sustain - v. to provide what is needed for (something or someone) to exist, continue, etc.
trajectory - n. used to describe a process of change or development that leads toward a particular result
migrate – v. to move from one place to live or work in another
straggler - n. : a person or animal that moves slower than others and becomes separated from them
calf - n. the young of various other large animals (such as the elephant or whale)
baby boom – expression. a time when there is a great increase in the number of babies born
all hands on deck – idiom. used to say that everyone is needed to help in a given situation
