My name is Lucy and this is my grandfather. His name is Tim and he is my best friend. My grandfather is 64 years old and he is retired now, so he has much time to be and play with me. I love him very much and I know he loves me too.

    He lives with me, my father, my mother and my brother Kevin. We live in a big house. My grandfather is a very tall and strong man! Can you see me on his shoulders (肩膀)in this picture? He is really strong! My grandfather always knows what I want to do or to eat or what I feel inside! When I am sad, he makes me laugh with his funny faces. Every night before I go to bed, my grandfather tells me stories, and he even sings for me!

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理发用的电吹风机中有电动机和电热丝，电动机带动风叶转动，电热丝对空气加热，得到热风将头发吹干．设电动机线圈的电阻为R₁，它与电热丝的电阻R₂串联，接到直流电源上．电吹风机两端电压为U，电流为I，消耗的电功率为P，则有（   ）

下列各句中，没有语病的一项是（    ）

如图1中矩形ABCD中，已知AB=2，AD=2$\sqrt{2}$，MN分别为AD和BC的中点，对角线BD与MN交于O点，沿MN把矩形ABNM折起，使平面ABNM与平面MNCD所成角为60°，如图2

（1）求证：BO⊥DO；

（2）求AO与平面BOD所成角的正弦值．