The correct answer here is D )That it is short and every day should be cherished and enjoyed.
Houseman here wants to encourage the reader to see beauty in every new day and enjoy life from all of its perspectives. The speaker in this poem is twenty years old and he makes a prediction that he will have about fifty more years of life left. In the last verse, it is evident that he is aware of the sad fact that this time is not enough for him to see everything he wants to see so he decides to cherish even the winter days when the cherry is not in bloom.