Final answer:
The correct sentence is B, where 'Darn' is capitalized as the first word of direct speech and the sentence ends with a period within the quotation marks. The dialogue is properly punctuated and capitalized, adhering to standard English grammar rules.
Step-by-step explanation:
The correct sentence is B: "As Jimbo tripped up the staircase he said, 'Darn, that hurts.'" When constructing a sentence where a character speaks, the first word of the direct speech should be capitalized. Additionally, a comma is typically used after said, before the beginning of the quotation.
However, in this case, since there's a description interposed, the comma is not present. It is also standard to end the speech with the appropriate punctuation inside the quotation marks, which can vary depending on the sentence structure, as in this case, a period is used. Furthermore, shouting or emphasis in dialogue, such as the use of all caps for 'HURTS', is often discouraged unless it is a creative choice that aligns with the tone of the work, which is why option D: "Darn that HURTS." is not the standard usage.