Little Red Riding Hood lives near a forest (森林). She often goes to visit her grandma. She usually brings her some food. One day, when she is on her way to her grandma's home, a wolf sees her. The wolf stops her and asks, “Where are you going?” “My grandma's home.” answers Little Red Riding Hood. The wolf suggests (建议）picking some flowers for her grandma. The wolf runs to her grandma's home first. He eats the grandma. He is lying (躺）in the grandma's bed. Little Red Riding Hood comes and the wolf wants to eat her. Little Red Riding Hood cries for help. A hunter (猎人）comes quickly. The wolf is afraid, and he runs away.

在三棱锥$P-ABC$中，$PA=PB=PC$，底面$△ABC$是正三角形，M、N分别是侧棱PB、PC的中点．若平面$AMN\perp$平面$PBC$，则平面$AMN$与平面$ABC$所成二面角（锐角）的余弦值等于(      )

控制人遗传性状的基因，位于细胞的哪一种结构上（    ）

计算：$\frac{m^2}{n^{2}p}$•（﹣$\frac{n{p}^2}{2m}$）=____