题目

A 15-year-old student who invented a flashlight(手电筒) getting power from the holder's body heat is going home today from California with a big prize and a chance to do further research. Ann Makosinski was the only Canadian among the four winners at Google's international science competition. Thousands of young scientists from around the world took part in the competition. Winning the science and technology competition was a surprise. Ann said, I think it will have a great influence on my future. Ann thanked her family for encouraging her interest in science and said that her first冻豆腐里面有小孔的成因是  （   ）A．豆腐自身冻缩而成 B．豆腐自身膨胀而成C．外界的冰雪扎进豆腐里而成 D．豆腐里面的水受冻先结冰，再熔化成水后而成