Read the procedural text. Connecting Your Phone to Speakers

Turn down the volume on your phone.
Locate the speakers' input cable. Most speakers are connected, and one has an input cable.
Turn down the speaker volume.
Plug the input speaker cable into your cell phone's headset jack.
Play a music file while you slowly turn up the speaker volume.
Which text feature, if added, would best aid the reader’s understanding of the passage?

statement of purpose
diagrams of phone and speakers
list of materials needed
sequenced, numbered steps