共用题干题

<p>根据下面资料，回答43-46题<br/>It was Sharing Day!The teacher had asked the students to bring something interesting to class．<br/>Jimmy found the little box he and Dad had made．Inside was a piece of rock，a sand dollar and a shark （鲨鱼）tooth．Nobody could have anything as interesting as these !<br/>In class，Jimmy waited anxiously，hoping to be called on first by the teacher．But Kara was first．<br/>She held up a sand dollar．Jimmy’s eyes grew big．<br/>"I found this on the beach，"Kara said．"It’s interesting．The little holes that make the sand dollar look like a flower are breathing holes．See all the needles？They help the sand dollar move and dig into the sand．"<br/>Jimmy was a little uneasy．Oh，well，he still had his rock and shark tooth．<br/>Then Mark stood up．"This is my favorite rock，called pumice （浮石）．"Then Mark dropped the rock into a glass of water．"Look !Pumice is the only rock that floats !"<br/>Jimmy put up his hand and waved，but the teacher called on Justin instead．<br/>"I found this shark tooth in Hawaii last Christmas，"Justin said．<br/>The class was excited，but Jimmy lowered his head．"Sharks have rows of teeth．Every time a shark loses a tooth，another one takes its place．"Justin passed the tooth around．<br/>Jimmy heard the teacher call him．He stood on one foot and then the other．"Well，ah，see．．．my treasure box is interesting !It was just a piece of wood until Dad and I cut it into pieces and finally made a box out of it．It smells good，reminding us of camping．"<br/>"What’s inside？"asked Lisa．<br/>Jimmy opened his box．"A sand dollar，a piece of pumice and a shark tooth．"<br/>His classmates’mouths dropped open．The teacher looked at the objects in the box and smiled．<br/>"Now that’s interesting !"he said．</p>

Who shared with the class a rock that floats？（）