Here, only I and II, if true, would weaken the author's claim that the community in question provides the girls with "no lessons in cooperation" and which in turn results in the girls wasting hours in bickering. If group games played by younger girls involves cooperation and the girls individually cooperate with their mothers in looking after babies, then the girls do receive lessons on cooperation. II is a bit illogical because girls cannot simply learn cooperation by looking and this is no lesson. So, the correct answer is option D.