Every year people celebrate the Spring Festival in China．Usually it is in January or February．It's the most important(重要的)festival in China．So before it comes，everyone buys many things，and they often make a special kind of food called dumplings-It means"come together"．Parents always buy new clothes for their children and children also buy presents for their parents．On the Spring Festival eve(除夕)，all the family members come back home. They sing, dance and play cards．When they enjoy the meal，they give each other the best wishes for the coming year．They all have a good time。

近几年来，大棚农作物养殖业蓬勃发展，为提高大棚农作物的结果率，在棚内放养了一些蜜蜂，这体现了动物在自然界中的作用是（    ）

几种物质的溶解度曲线如右图。则下列说法正确的是（   ）