The document discusses several grammatical concepts: 1) It contains examples of interrogative statements using phrases like "Is there..." and "Are there..." 2) It explains the difference between the modal verbs "can" and "could", where "could" is the past form of "can" but also expresses possibility or hypothetical situations. 3) "Can" and "could" are used to express the progressive or continuous aspect of verbs like "see", "hear", and "understand".