Chapter 19, Problem 10RA

The increased intestinal absorption of calcium is stimulated directly by

$\begin{array}{l}\text{a}\text{. parathyroid hormone}\text{.}\hfill \\ \text{b}{\text{. 1 ,25-dihydroxyvitamin D}}_{\text{3}}.\hfill \\ \text{c}\text{. calcitonin}\text{.}\hfill \\ \text{d}\text{. all of these}\text{.}\hfill \end{array}$