The number of sentences per exercise can vary depending on the specific exercise and the level of complexity. In general, exercises can range from 1 to 5 sentences, with some more complex exercises containing up to 10 sentences. The number of sentences in an exercise is typically determined by the learning objectives and the specific skills being targeted. **

It depends on the context and the purpose of the writing. Series of sentences are more straightforward and easier to understand, making them suitable for conveying simple ideas or information. On the other hand, complex sentences are more sophisticated and can convey more nuanced or detailed information, making them suitable for more formal or academic writing. Ultimately, the choice between series of sentences and complex sentences should be based on the complexity of the content being communicated and the intended audience. **

Simple sentences consist of a single independent clause, which means they have only one subject and one verb. Compound sentences are made up of two independent clauses joined by a coordinating conjunction or a semicolon. Compound-complex sentences contain at least two independent clauses and one or more dependent clauses. These clauses are joined by coordinating conjunctions and subordinating conjunctions. By analyzing the structure and the presence of independent and dependent clauses, it is possible to distinguish between these three types of sentences. **

This question is asking for the number of sentences in the response. **

This response contains four sentences. **

Simple sentences consist of a single independent clause that expresses a complete thought. They typically have a subject and a verb and do not contain any dependent clauses. On the other hand, compound sentences are made up of two or more independent clauses that are joined together by coordinating conjunctions like 'and', 'but', or 'or'. Compound sentences allow for the combination of multiple related ideas into a single sentence. **

To transform English active sentences into passive sentences, you typically move the object of the active sentence to the subject position in the passive sentence. The subject of the active sentence becomes the agent in the passive sentence, and the verb is changed to a passive form (usually a form of "be" followed by the past participle of the main verb). Additionally, the original subject of the active sentence can be included in the passive sentence with a preposition such as "by." **

To change an English active sentence into a passive sentence, you need to make the object of the active sentence the subject of the passive sentence. The subject of the active sentence becomes the agent in the passive sentence (if included). The verb in the active sentence is changed to a form of 'be' followed by the past participle of the main verb. Additionally, any prepositions or other necessary words should be included in the passive construction. **