This is not the first time I've read this book and it won't be the last. However, it has been a few years since I'd read it from cover to cover. Last night, it just felt right.
Essential English Grammar reviews the basic parts of a sentence and how they function. It's a great reference guide and teaching tool. The book includes insight into sentence structure and includes practice work. As a blogger, writers, and even a reader, I've found this book to be a fantastic resource.
p.s. Essential English Grammar does not teach punctuation rules or any of that jazz. This book strictly tells you what a sentence should be and how words should behave within said sentence.
The demonstrative pronouns of English are this (plural these), and that (plural those), as in these are good, I like that. Note that all four words can also be used as determiners (followed by a noun), as in those cars. They can also form the alternative pronominal expressions this/that one, these/those ones.
The interrogative pronouns are who, what, and which (all of them can take the suffix -ever for emphasis). The pronoun who refers to a person or people; it has an oblique form whom (though in informal contexts this is usually replaced by who), and a possessive form (pronoun or determiner) whose. The pronoun what refers to things or abstracts. The word which is used to ask about alternatives from what is seen as a closed set: which (of the books) do you like best? (It can also be an interrogative determiner: which book?; this can form the alternative pronominal expressions which one and which ones.) Which, who, and what can be either singular or plural, although who and what often take a singular verb regardless of any supposed number.