#### Answer

(a) and (b) are functions
(a) is one-to-one

#### Work Step by Step

To determine if a graph is a function, we use the vertical line test. Graphs (a) and (b) pass the vertical line test and are therefore functions. To determine if these functions are one-to-one, we use the horizontal line test. Graph (a) passes this test and is therefore one-to-one.