The service that can complete a paragraph based on a sentence is Azure OpenAI. According to Microsoft Learn's AI-900 study guide, Azure OpenAI provides access to advanced language models like GPT-3.5 and GPT-4, which can generate and continue text, summarize, or create content based on prompts. The task described-text completion-is precisely what GPT models are designed for.
Azure AI Language performs language understanding and analysis (sentiment, key phrases, translation), Azure Machine Learning trains custom models, and Azure AI Vision handles images. Hence, Azure OpenAI is the correct choice.