試題詳解

49. The vascular system of a three-year-old dicot stem consists of
(A) 3 rings of xylem and 3 of phloem.
(B) 2 rings of xylem and 2 of phloem.
(C) 3 rings of xylem and 1 of phloem.
(D) 1 rings of xylem and 3 of phloem.
(E) 2 rings of xylem and 3 of phloem.