Vascular Plants Are Thought to Be the Result of a Single

Vascular plants are thought to be the result of a single evolutionary event: the evolution of a wholly new cell type, the tracheid. This cell type

A) provides a mechanism for the storage of a new type of carbohydrate, starch.
B) is the first cell type to contain chloroplasts.
C) permits fertilization in the absence of water, thus permitting plants to invade dry habitats.
D) forms the seed.
E) is the principal water-conducting element of the xylem in all vascular plants except for the angiosperms.