John usually goes to school by bus. He leaves (离开)his house at seven and gets to school at about seven twenty. His school is on the hill.

    From Monday to Friday John usually has four classes every day. He likes English. He wants to be an English teacher. He hopes he will go to the USA to study English one day. On Sundays, he often goes to the library with his friends, but sometimes they go to see movies.

分解因式：a²﹣4b²=____．

已知AC⊥BC，AC=BC，D满足$\overrightarrow{CD}$=t$\overrightarrow{CA}$+（1﹣t）$\overrightarrow{CB}$，若∠ACD=60°，则t的值为（　　）

禹的儿子启继承父位，“公天下”变为“家天下”，____制开始。

如图三幅图是表示地球演变过程中海陆分布的变化情况，根据大陆漂移的假说，由早到晚的排列顺序是（    ）