#9 would be Cactus Spines. The other two options are considered to be chemical defenses, not structural.
#10 is C.) Giraffes have a long, mobile tongue that can maneuver between the thorns. While their saliva does play a role in their ability to eat the leaves, they can't completely dissolve the thorns. It simply coats them so that they do not hurt as much if the giraffe is unlucky enough to have caught one.
Fun-fact...that's why giraffe tongues are blue! They need to maneuver between the thorns, so they tend to get a lot of time in the sun. The dark color helps to prevent against sunburns.
Hope I could help! :)
