我国南方与北方自然环境差异大，下列描述正确的是（   ）

弹簧上端固定，下端悬挂一根磁铁，将磁铁抬到某一高度放下，磁铁能上下振动较长时间才停下来，如图甲所示．如果在磁铁下端放一个固定的铁制金属圆环，使磁铁上、下振动穿过它，能使磁铁较快地停下来，如图乙所示．若将铁环换成超导环如图丙所示，可以推测下列叙述正确的是(    )

$\sqrt{79}$的值介于2个连续的整数n和n+1之间，则整数n为（　　）

 Tim was reading a book at office. Someone knocked on the door. He opened the door.____  .
"My name is Rebecca," said the lady. "You've got to help me!"
"Take it easy." ____ "What happened?"
"My grandma died last month. She left all her money, about $1,000,000 to me. She told me she had saved the money in a bank.____ . "
"But yesterday when I went to the bank, I only got an envelope with nothing in it. he money is gone!"
Rebecca took the envelope out of her handbag and gave it to Tim.
Tim looked at it carefully under the light. It was just an envelope with two old stamps on it. ____ 
“Don't worry, Rebecca," he said. "Your money is still here.”