图中，同在冬季，两位同学的衣着不同．造成这种现象的主要因素是（ ） A．海陆位置

Every new thought or idea has to be connected to what we already know. Unfortunately, it is easy to limit the possibilities of a new idea by connecting it to only one area of our previous knowledge. Great thinkers are aware of this and try to combine new and old ideas in as many different ways as possible. They also try to make connections that may seem strange at first. By comparing and connecting ideas and objects in new ways, creative thinkers are able to think of new applications and solutions. Many of the things that we use every day were invented by someone who saw similarities between his or her ideas and objects or systems in the world.

双胎妊娠在妊娠期常见并发症为：______、______、______及______。

我国要长期稳定以家庭承包经营为基础、统分结合的双层经营体制，其关键和基础是( )。

A．加快农村经济体制改革

B．提高农业的生产力水平

C．稳定和完善土地承包关系

D．完善农业社会化服务体系

家禽的骨软化症是由于（）。

A、钙缺乏

B、磷缺乏

C、铁缺乏

D、硒缺乏