There is _______ corn in the house.

----- __________it be Li Ping who broke the glass?
---- No. It __________ be Wu Dong who did it.

阅读理解
    Recently, an Internet game has become a new fashion among young office workers and students. People can “farm” on a piece of “land” and “grow”, “sell” or even “steal” “vegetables”, “flowers” and “fruits” on the Net. They can earn(挣) some e-money and buy more “seed”(种子), “pets” and even “houses”.
    Li You from Xi'an said people in the city get tired from work, they go to their own farms, take care of their crops(庄稼), and pull out weeds(杂草). It is glad to forget about the pressure in cities.
    Li Bu grew up in a small village, and then he went to a city, but now he misses the life in the village and “Happy Farms” makes the country dream possible in his office. He said every time he sees his crops, dogs, and grasses, he feels like he is in the village again. When he is working on his farm, he can feel the breath of nature, and get happiness from farming and harvesting(收获).
    Li Lei enjoys putting some “bugs”(虫) in my friends' garden and they've become closer because of the game. Having fun together is the most exciting thing about it.
    Li Hong said it was just a waste of time. Teenagers spend so many hours on it and they can't focus on their study.

某小组同学研究金属球在水中受到浮力的大小时，提出不同的猜想。猜想Ⅰ：金属球在水中所受的浮力F_浮跟金属球的密度有关；猜想Ⅱ：金属球在水中所受的浮力F_浮跟金属球浸入水中的深度有关。于是他们将半径均为5厘米但密度不同的金属球甲、乙分别挂在测力计下，将其逐步浸入水中进行实验。他们通过测出球心到水面的距离h来表示金属球浸入水中的深度、并读出相应的测力计示数F且计算得出F_浮，实验数据分别见表一、二。


① 该小组所进行的序号为1、7实验的示意图是图11中的____ 。（选填“a”或“b”）
② 分析比较实验序号2~6或8~12的实验数据及相关条件，可初步得出的结论是：同一金属球浸入水中的深度增加时，所受到水的浮力____ 。
③ 分析比较实验序号2和8、3和9、4和10或5和11的实验数据及相关条件，可初步得出的结论是：____ 。并由此可知，金属球在水中所受的浮力F_浮跟金属球的密度无关。
④ 他们进一步提出问题：金属球在水中所受最大的浮力跟哪些因素有关？为继续研究，最需要添加的实验器材是：跟甲（或乙）____ 不同的金属球。（选填“半径”、“密度”或“质量”）

(2010·湖南理，4)在Rt△ABC中，∠C＝90°，AC＝4，则·等于(　　)