Final answer:
A complex sentence contains an independent clause and at least one dependent clause.
Step-by-step explanation:
A complex sentence is a sentence that contains an independent clause and at least one dependent clause. In the given options, the correct complex sentence is: As industrial robots became more common, many laborers who lacked skills lost their jobs. This sentence has an independent clause 'many laborers who lacked skills lost their jobs' and a dependent clause 'As industrial robots became more common' which cannot stand alone as a complete sentence.
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