已知PA、PB分别切⊙O于A、B，E为劣弧AB上一点，过E点的切线交PA于C、交PB于D．

    A poor farmer had a friend,who was famous for the wonderful apple he grew.One day,his friend gave the farmer a young apple tree and told him____(take) it home and plant it.

    The farmer was pleased with the gift,but when he got home he did not know where to plant it.He was afraid that ____he planted the tree in one of his fields,his neighbors would come at night and pick some of the apples.Finally he planted the tree in his wood____no one could see it.But____sunlight and good soil,the tree soon died.

    Later the friend asked the farmer why he had planted the tree in____a poor place."What's the difference?"the farmer said____(angry)."If I had planted the tree near the road,strangers____(steal) the fruit."

    "Yes,"said the friend,"____at least someone could have enjoyed the fruit.Now you not only have robbed everyone____the fruit,but also you____(destroy)a good apple tree!"

下列各数中是无理数的是（　　）

把方程x²+6x+3=0变形为（x+h）²=k的形式，其中h，k为常数，则k=____．