Follow these steps to make a sine wave:
Follow the first five steps in the semicircle exercise to create a circle with a line through it. This time, though, make it horizontal.
Click once to select the bottom half of the circle; then click and drag it away from the line.
Remove the horizontal line.
Click once to select the bottom image. Then click and drag from its left end point and snap it to the right end point of the top image.
Copy and paste everything. Then select and drag to extend the cycle. Repeat this process to add as many waves as desired.
When you're finished, you can scale the width or height of each wave however you want.