Differentiate between gastrovascular cavity and alimentary canal

Which best describes the structure of dna?

Ialready know the answers to these questions and they are on the attachment. but i just need to know why that answer is the correct one. plz asap! this is for a report that i need to email by 10!

Draw the farm's ppf for corn and beef. draw a point that shows an inefficient combination of corn and beef. label ita. draw a point that shows an unattainable combination of corn and beef. label itb. draw a point that shows an efficient combination of corn and beef. label itc.