69＋6=____

直线l₁的方向向量为 $a=(1,2)$ ，直线l₂的方向向量为 $b=(1,-3)$ ，那么l₁与l₂所成的角是（   ）

B

    One day, a farmer was walking along a road with his son Thomas when they saw a horseshoe (马蹄铁) on the ground. The father said to his son, “Look at the horseshoe on the ground. Go and1the horseshoe and put it in your bag, my son.” But Thomas said, “If I do so, it will waste my time.” His father said2but picked it up himself. When they3a nearby town, they had a rest. There the farmer sold the horseshoe and 4some strawberries with the money.

    The father and the son went on walking. The sun was well up in the sky.They soon 5all their water and there was not a house or even a tree for them to have a rest. Thomas felt6thirsty to walk on. At this time, his father gave him a strawberry and he quickly ate it. After a while, his father gave him7strawberry and once again, his son got it quickly and put it in his mouth.

    And so they went on.The old farmer gave the strawberries and the son ate them. When Thomas had eaten up all the strawberries, his father said to him, “My dear son,8you picked up that horseshoe, you would have your own9to eat. Always remember the lesson: if you don't worry about the little things, you will find it10to do the great things.