My grandpa has a farm. The farm is very big and beautiful. There are many animals on the farm. There are ten horses, seven goats, nine cows and many hens. The cows are black and white. The goats are white. The hens are very fat. My grandpa likes vegetables. So  there are a lot of potatoes, green beans, carrots and tomatoes. I like potatoes. My sister likes green beans. We all like this farm very much.

①唐朝国家统一，社会安定

②唐朝经济、文化世界领先

③唐朝对外政策开放开明

④唐朝对外交通发达

下列有关煤、石油的说法正确的是（　　）

下图一是研究不同浓度的生长素对幼根生长影响的实验结果，图二表示利用玉米胚芽鞘研究生长素的植物体内运输方向的实验设计。下列说法正确的是（）