Final answer:
The correct answer is 'but plan to learn before we leave for Venice.' A dependent clause is a clause that cannot stand alone as a complete sentence because it does not express a complete thought.
Step-by-step explanation:
The correct answer is: but plan to learn before we leave for Venice.
A dependent clause is a clause that cannot stand alone as a complete sentence because it does not express a complete thought. It relies on an independent clause to make sense. In the given passage, 'but plan to learn before we leave for Venice' is a dependent clause because it starts with the subordinating conjunction 'but' and relies on the main clause 'I cannot swim' to complete its meaning.