In Part A, the presence of the simile is comparing the daffodils to the stars by using a comparison through the comparison word "as". The characteristic that the author is comparing is continuous. Something continuous never ends; therefore, the correct answer is that the simile describes the endless rows of daffodils.
In Part B, the mood that the author creates through the use of the simile mentioned in Part A is C: energetic. In the sample sentence, the word twinkle implies movement, and this movement indicates that being energetic is one of the characteristics of the daffodils.