in the reading, what is the cry "S-t-e-a-m-boat a-comin'!" an example of dialect. Option D is correct.
A dialect is defined as a form of the language that is spoken in a specific region of the country or by a particular group of people. There exist a number of different dialects of English and they have different words and grammar.
In this particular case, the word "coming" does not include the G at the end of it which is necessary since the verb "come" should have an "ing" at the end to be properly conjugated according to English grammar rules. So, we can infer that it is a particular form of the language embraced in certain region.