clause

[Ju]

(quoted)
Dependent clauses have a subject doing a verb, but they have a subordinate conjunction placed in front of the clause. That subordinate conjunction means that the clause can't stand independently by itself and become a complete sentence. Instead, the dependent clause is dependent upon another clause--it can't make a complete sentence by itself, even though it has a subject doing a verb. (unquoted)

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What does it mean of it has a subject doing a verb?

Ju

[Afit]

Dependent clauses have a subject doing a verb

It means each clause has a verb and to each verb belongs a subject.