Main clauses express a complete thought and appear in compound, complex and compound-complex sentences. Therefore, the correct answer is all of the above. A compound sentence is made up of two independent clauses which are joined by a coordinating conjunction. A complex sentence is made up of an independent clause and a dependent clause which are joined by subordinating conjunction. A compound-complex sentence is made up of two or more independent clauses and one or more dependent clauses.
That would be a practical exercise. Practical means the actual doing or use of something rather than with theory and ideas. So it would apply to real life situations.
