⑴Mom and Dad are the most important people in your life. They have been looking after you since you were born. ⑵你应该一直爱他们。You should also get on well with them. But some children don't know how to do this. Here are some ways to help you. Spend more time with your parents. ⑶Don't spend too much time playing computer games or watching TV. Ask your parents to play with you. ⑷和他们交谈或者散步。 Be kind to your parents. You can make them happy with a smile when you come home. You can send your mother a card on Mother's Day or tell your father a joke on his birthday. ⑸You can also clean your room by yourself. Work hard. If you do your best in your studies, your parents will be proud of you.

N_A表示阿伏加罗常数的值，下列说法正确的是（    ）

第一次世界大战期间，德国等缺乏原材料的国家，大力发展化学合成技术，从而推动了化工技术的发展。这说明的根本问题是（    ）