Answer:
- tusks; a
 - carvings; they
 - materials; this
 - away; first
 - shape; thus
 - ivory; another
 - ivory; this
 - beautiful; however
 - soapstone; this
 - walrus; they
 
Step-by-step explanation:
In this particular exercise, look at where the first sentence appears to pause or end; that is where you add the semi-colon. It is typically used to connect 2 short & related sentences; thus, it is often utilized to add commentary. 
Obviously there are better examples than the ones I used above, but I hope this helps!