如图，直线l₁∥l₂∥l₃，直线AC分别交l₁、l₂、l₃于点A、B、C，直线DF分别交l₁、l₂、l₃于点D、E、F，AC与DF相交于点H，且AH=1，HB=2，BC=5，则 $\frac{DE}{EF}$=____

函数y=﹣cos（$\frac{x}{2}$﹣$\frac{\mathrm{\pi }}{3}$）的单调递增区间是（　　）

    No one loves me more than my parents, especially my father. My father is stout and strong, severe look on his face and keen expressive eyes. At first sight you may feel him hard____ (approach). In fact, he is very kind and considerate. I believe my father is a____ (talent) man. He decisive and efficient in doing things. By his own talents and years of efforts, he____ (provide) the family with a good social position and a____ (relative) rich life. Besides, he lives in harmony____ others and never quarrels with anyone, so people from all walks of life come to my house, from____ I've gained lots of social experience. But at home he is a strict parent who is hard on me and has high____ (expectation) of me. I can see that my idling away time____ (hurt) him deeply, while if I have done something great and meaningful, such as____ (write) a book, he will be more excited than me. I always remind myself I must go on and on, and never ____ I give up halfway.

按要求写出下列反应的化学方程式．
①氯化钡溶液与稀硫酸混合： ____ ；
②碳酸钾溶液与稀盐酸混合： ____ ；
③氢氧化钡溶液与稀硝酸混合： ____ 。