引出施事、受事：由

In Chinese, the word "由" (yóu) is used to introduce the agent (施事) or the doer of an action in a sentence, as well as to indicate the patient (受事) or the receiver of the action. This structure is particularly useful for emphasizing who is responsible for an action or task.

For example:

• In the sentence "这道题由你来回答吧" (Zhè dào tí yóu nǐ lái huídá ba), "由" introduces "你" (you) as the agent responsible for answering the question. The focus is on who will perform the action.
• In "这件事情由班长负责" (Zhè jiàn shìqíng yóu bānzhǎng fùzé), "由" indicates that "班长" (the class monitor) is the one responsible for the matter, highlighting the agent's role in the situation.

Using "由" helps clarify the relationship between the agent and the action, making it a valuable structure in Chinese grammar for expressing responsibility and agency.