①市场竞争导致商品优胜劣汰
②商品使用价值会影响人的消费选择
③功能不同的商品会相互替代
④商品使用价值因替代品出现而减小
A:①②
B:①③
C:②④
D:③④
小华吃西瓜时不小心把一些西瓜籽吞进肚里了,最终这些西瓜籽会随粪便排出体外。这些粒瓜籽在小华体内经过的部位依次是( )
已知关于x,y的方程组2x+3y=k3x+4y=2k+1满足方程x+y=3,求k的值.
从方框中选择适当的单词完成短文。
What's this on the table? It is a ____ of my new classroom. ____ at the picture. ____ can you see ____ the classroom? I can see a ____ desk in the front of the classroom. Some books are ____ the desk. I can see two white ____ , too. There are____ colored chalks (彩色粉笔n them. ____ is the broom (扫帚)? It’s ____ the door. I like this new classroom.