据统计，从1840年至1894年，我国粮食商品率由10%增长到16%。出现这一状况的主要原因是（   ）

    During holidays，Kitty usually goes to see the exhibits in many museums，such as the history museum，the art museum，the museum of science and technology and the museum of natural history．There are thousands of wonderful things in museum.There are paintings，sculptures(雕塑)，costumes(服饰)，swords(剑)，ancient animal bones and plants，stuffed animals(动物标本)and many others．It is always a good review of history to visit those museums．It is also a great way to learn more things by myself．

读“某区域等高（深）线示意图”，完成下列问题。

良好的用眼习惯可以预防近视．下列习惯中，不利于预防近视的是（    ）