Hi there!
A t-shirt sounds awesome! Here are a few suggestions:
-a favorite animal
-a meme
-a quote
-an inspirational person
-abstract work
-a piece of your own artwork
-a block design
Hope this helps!! :)
D is the correct answer.
In the badly drawn diagram attached, you will find the <em>yellow</em> represents wavelength, which is the distance between identical points on consecutive waves.
The <em>green</em> represents the amplitude, which is the distance between the origin (middle) and crest/trough (top/bottom)
The Mound Builders used metal tools, and were probably metal builders. Based on that information I would say the answer is B.Copper, because copper is a metal.
They are both string instruments.