Question

later in the season, when the carrot has developed leaves, where is the source?
the mature leaves
the root
the stem
rewatch

Explanation:

In plant biology, a "source" is a tissue that produces and exports organic nutrients (like sugars from photosynthesis). Mature leaves perform photosynthesis to make these nutrients, so they act as the source once they develop. The carrot root is a storage sink, not a source when leaves are active.

Answer:

The mature leaves