Suppose I follow person B who doesn't follow me. If I want to send to person B a tweet of person C from an unrelated conversation, how do I do it? I tried "reply @B" but it didn't show the link. I tried "retweet" but I can only retweet to myself.
When you retweet (unless your account is protected) the tweet is publicly visible. If you mention someone in a tweet who does not follow you they will not receive an instant notification, but it will appear in their "Mentions and Interactions" tab.
So, if you quote the tweet of person C with a mention of @personB the tweet will appear in the Mentions and Interactions tab of personB
Twitter Support describes this in their "Type of Tweets and where they appear"
Definition: A Tweet containing another user's Twitter username, preceded by the "@" symbol, like this: Hello @NeonGolden! What's up?
Where it appears for the sender: On the sender's profile page of public Tweets.
Where it appears for the recipient: In the recipient's Mentions and Interactions tabs, which is accessible only by them. Additionally, mentions will appear in the recipient's Home timeline view (not on their profile) if they are following the sender. Note: Anyone on Twitter who is following the sender of a mention will see the Tweet in their Home timeline.
Places it will never appear: On anyone's profile page, unless they wrote the message.