Rearrange the following sentences in the proper sequence to form a meaningful paragraph and then answer the questions given below.
A. These beautiful orange and black insects travel thousands of miles to reach their wintering grounds in central Mexico. 
B. Remarkably, no single butterfly completes the entire round trip; it takes several generations to achieve this feat. 
C. Ultimately, their great-grandchildren will be the ones to arrive back in the original northern breeding grounds, continuing the cycle. 
D. The late summer generation is the one that undertakes the monumental journey south, developing a unique physiology that allows for this extended flight. E. The migration of monarch butterflies across North America is one of nature’s most astounding phenomena.  F. They spend the winter clustered in oyamel fir forests, covering the trees in a thick, living carpet.  G. As spring approaches, these same butterflies begin the return trip north, laying eggs along the way.  Which of the following is the FIRST sentence after rearrangement?