什么时候不用to

phrasal verb – n. a group of words that functions as a verb and is made up of a verb and a preposition, an adverb, or both

infinitive verb – n. the basic form of a verb with the word "to"

key – n. something that is necessary in order to do or achieve something

vineyard – n. a field where grapes are grown

precede – v. to happen, go or come before something

gerund – n. a noun ending in -ing

password – n. a secret series of numbers or letters that allows you to use a computer system

causative – adj. making something happen or exist : causing something