1. I'm very excited to hear from my parents.
该句的重点是收到某人的来信 其固定词组是hear from
2. It's so necessary for children to learn English well.
该句是明显的it's necessary+for sb+to do sth 意为有必要做某事
3. Thank you for looking after my puppy.
此句用到Thank you for doing sth 意为感谢某人做某事
4. It's impolite to come in without knocking at the door.
it's +形容词+（for sb）+to do sth
5. It takes them five hours to put out the fire.
it takes sb +时间 花了某人多少时间做某事
翻译的话,要重点提取句子中隐藏的词组,这样的话,整体结构就不会出现错误.
请参考! 1. I'm very excited to hear from my parents.
该句的重点是收到某人的来信 其固定词组是hear from
2. It's so necessary for children to learn English well.
该句是明显的it's necessary+for sb+to do sth 意为有必要做某事
3. Thank you for looking after my puppy.
此句用到Thank you for doing sth 意为感谢某人做某事
4. It's impolite to come in without knocking at the door.
it's +形容词+（for sb）+to do sth
5. It takes them five hours to put out the fire.
it takes sb +时间 花了某人多少时间做某事
翻译的话,要重点提取句子中隐藏的词组,这样的话,整体结构就不会出现错误.
请参考!