Option A ('Animal testing is cruel because animals suffer horrible deaths.') is an example of a complex sentence as it contains an independent clause and a dependent clause linked by the subordinating conjunction 'because'.
Among the options provided, Option A is an example of a complex sentence. This is because it contains one independent clause ('Animal testing is cruel') and one dependent clause ('because animals suffer horrible deaths'). The dependent clause starts with the subordinating conjunction 'because', which introduces the reason for the cruel nature of animal testing, thus making the sentence complex.
Complex sentences are important in academic writing as they allow the writer to connect ideas and convey more nuanced information. They can show relationships between ideas such as cause and effect, provide additional details, or offer explanations. In the context of discussing animal testing, complex sentences can help to present a well-reasoned argument regarding the ethical considerations of the practice.