Which of the following is a region that produces cells in a plant?
a. cork cambium
c. vascular cambium
b. apical meristem
d. all of the above

Cork cambium, apical meristem, and vascular cambium. so the answer is d
the  cork cambium  is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems.   the  vascular cambium   (plural cambia) is a plant tissue located between the xylem and the phloem in the stem and root of a  vascular  plant, and is the source of both the secondary xylem growth. a  meristem   at the tip of a plant shoot or root that produces auxin and causes the shoot or root to increase in length. growth that originates in the  apical meristem   is called primary growth.

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Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.