有關英文一問？5點

Because it is a special term, but it is not used as conjunction.

E.g: Text-messaging
You cannot say Textmessaging or Text messaging either, so it is SPECIAL, but not to link 2 nouns.

Text-messaging is not 2 nouns link together, it's a term/ noun.

Hope that i can help u!

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時在兩個英文字中間會有-?例如text-messaging
中間會有-= it usually links up two noun.