These words all mean to see sth, especially when you pay careful attention to it. 以上各词均含看到、注意到之义。

• notice to see, hear or become aware of sb/sth; to pay attention to sb/sth 指看（或听）到、注意到、意识到、注意、留意：◆The first thing I noticed about the room was the smell. 我首先注意到的是这屋子里的气味。
• note (rather formal) to notice or pay careful attention to sth 指注意、留意：◆Please note (that) the office will be closed on Monday. 请注意办事处星期一将关闭。 NOTE This word is very common in business English. 该词在商务英语中非常通用：◆Note that the prices are inclusive of VAT. 注意这些价格含增值税。
• detect to discover or notice sth, especially sth that is not easy to see, hear, etc. 指发现、查明、侦察出：◆The tests are designed to detect the disease early. 这些检查旨在及早查出疾病。
• observe (formal) to see or notice sb/sth 指看到、注意到、观察到：◆Have you observed any changes lately? 最近你注意到什么变化没有？◆The police observed a man enter the bank. 警察注意到一个男人走进了银行。
• witness (rather formal) to see sth happen 指当场看到、目击：◆Police have appealed for anyone who witnessed the incident to contact them. 警方呼吁目击这一事件的人与他们联系。

Patterns

• to notice/note/detect/observe that/how/what/where/who…
• to notice/observe/witness sth happen/sb do sth