Answer: where is the question?
The line demonstrating the use of an understatement is the following:
<em><u>BOB (still looking out—looks up): Still all right up above, though. </u></em>
Having read the previous lines, the reader gets the sense that the situation is critical, the water is rising and it has already flooded the whole lower part of the hotel. However, Bob wants to diminish the emergency of the situation by stating that the upper part still looks alright meaning that the extent of the damage is not as great as Ed says.
Of grammar rules but the basic ones refer to sentence structure and parts of speech, which are noun, pronoun, verb, adjective, adverb, preposition and conjunction. Let’s look at the way sentences are put together and the words that form them.

Basic English Grammar Rules
Some of the most basic and important English grammar rules relate directly to sentence structure. Some of these rules specify that:
A singular subject needs a singular predicate.A sentence needs to express a complete thought.
Another term for a sentence is an independent clause.
Clauses, like any sentence, have a subject and predicate too. If a group of words does not have a subject and predicate, it is a phrase.If they can stand alone and make a complete thought, then they are independent and called sentences.If they do not express a complete thought, they are called "dependent clauses." An example of a dependent clause, which is not a sentence, is “when i finish my work”.
A teacher. Im not sure you would learn this in English
