Chapter 13, Problem 3RA

The "lub," or first heart sound, is produced by closing of

$\begin{array}{l}\text{a}\text{. the aortic semi lunar valve}\text{. }\\ \text{b}\text{. the pulmonary semi lunar valve}\text{. }\\ \text{c}\text{. the tricuspid valve}\text{. }\\ \text{d}\text{. the bicuspid valve}\text{. e}\text{. both AV valves}\text{.}\end{array}$