To create a complex sentence, we need an independent clause and at least one dependent clause. Among the given options, 'Although designing shoes is hard work, it will pay off in the end.' is the complex sentence because it has both an independent and a dependent clause.
To combine the given sentences into a complex sentence, we need to use one independent clause and one or more dependent clauses. In the examples provided:
- 'Designing shoes is hard work, but it will pay off in the end.' is a compound sentence because it connects two independent clauses with the conjunction 'but'.
- 'Designing shoes is hard work; however, it will pay off in the end.' is also a compound sentence joined by a semicolon and a conjunctive adverb 'however'.
- 'Designing shoes is hard work; it will pay off in the end.' is a compound sentence joined by a semicolon.
- 'Although designing shoes is hard work, it will pay off in the end.' is indeed a complex sentence as it includes an independent clause 'it will pay off in the end' and a dependent clause 'Although designing shoes is hard work'.
Therefore, the sentence that successfully combines the initial statements into a complex sentence is 'Although designing shoes is hard work, it will pay off in the end.'