An imperative sentence expresses a request, command, order, instruction, or advice. Option 2 ('Please bring me a glass of water.') is a polite request starting with 'Please', making it an imperative sentence. Option 1 is an exclamatory sentence because it expresses strong emotion and ends with an exclamation mark. Option 3 is an interrogative sentence as it asks a question. Option 4 is an assertive (declarative) sentence because it states a fact.