如图所示，两半径相同的通电圆环导线互相垂直地竖直放置，圆心都在O点，通过的电流方向如图，电流大小都为$I$，其中直径AB恰好沿东西方向，则关于圆心O点的磁感应强度B的方向说法正确的是（    ）

某地区有7部电话，要使这7部电话都能互相通话，如果使用交换机需要多少对电话线（　　）

    Mary works in a bank. She is ____ busy every day that she____ no time to make dinner. There is a(n)____near Mary's house. After Mary comes back home from work, she likes to go to the restaurant____dinner.

    One day,____ Mary was in the restaurant, she saw____old man next to her looking for (寻找)something on the floor(地板).Mary felt surprised. So she____the old man.

    "____are you looking for?"

    "Oh, a piece(块)of bread," the man answered.

    "A piece of bread? Oh, the floor is so____.Please take this piece." Mary gave(给)a big piece of bread to the old man.

    "But my teeth____in that piece of bread."

  220年，曹操在洛阳称帝，改国号为魏。（  ）

每年4月6日是“国际枕头大战日”，人们纷纷带上枕头，在漫天羽毛和欢笑声中，开心“互殴”，享受这个“减压聚会”。这种调节情绪的方法是（    ）