Q6: A
Q7:D
Q8:C
Reasoning
Q6: Based on all the other questions talking about common ancestors I deduced that to find a “common” ancestor they need to find things that are the same.
Q7: All arthropod have a exo skeleton for example a lobster or crab. They all have a head, abdomen and thorax for example ants. They all have legs with joints for example a spider.
Q7:So bones are traveled down by ancestors so the types of bones stay the same but natural selection has changed them to better fit their environment.