Answer:
It is the first one: Be sure to watch the sick child carefully, please.
Explanation:
December is to winter as September is to Fall (or Autumn).
The Washington Monument is a famous building in the United States of America. It is located in Washington DC.
I believe a motif can contribute to, or become a theme when it gathers larger significance throughout a text. A theme is what you generally write about in a literary piece, so if you develop a metaphor further, it may come to denote a theme of a work.