C is the choice I would make because I believe the writer is planning to answer this question: "and how come we think dogs are so smart". The writer never tells us what dogs can't do (a) or mention others being dumb (b) and doesn't make fun of humans (d)
About 30 mintues, it helps yyyou develop I'm reading and makes your brain stronger
B.
it seems to have a good use of a quotation markers
a is missing the quotation marks
c is missing the quotation mark too
and d is missing one
so i go with b :) <span />
The answer for number six is B.