There are many types of big data, including structured, semi-structured and unstructured data, such as weblogs, audio, video, pictures and geographical locations. Structured data refers to data stored in a database, which can be represented by a two-dimensional table structure; Unstructured data refers to data with irregular or incomplete data structure and no predefined data, including office documents, texts, pictures, reports, images, audio information and video information in all formats. So b is wrong.