The correct answer is: a) Classical literary Tamil.
Sen-Tamil is the oldest form of Tamil, which was used in classical literature. It is a highly developed language with a rich vocabulary and complex grammar. Sen-Tamil is still used today in some religious and literary contexts, but it is not the everyday language of most Tamil speakers.
Modern spoken Tamil is a much simpler language than Sen-Tamil. It has a smaller vocabulary and a less complex grammar. Modern spoken Tamil is the language that is used in everyday conversation and in most forms of media.
Regional dialects of Tamil are variations of the language that are spoken in different parts of Tamil Nadu and Sri Lanka. These dialects can differ from each other in pronunciation, vocabulary, and grammar.
Tamil influenced by Sanskrit is a form of Tamil that has borrowed words and grammatical features from Sanskrit. This type of Tamil is often used in religious and philosophical texts.
I hope this helps!