动词Let, Allow和Permit

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informal – adj. not suited for serious or official speech and writing

formal – adj. suitable for serious or official speech and writing

negative – adj. referring to a word or statement that means "no" or that expresses a denial or refusal

mention – v. to talk about, write about or refer to something or someone, especially in a brief way

handbook – n. a small book of instruction or guidance on a subject

pet – n. an animal, such as a dog, cat, bird, or fish, that people keep mainly for pleasure