Which underlined word is spelled correctly in the following options?

The underlined word "its" in the given sentence is spelled correctly as it refers to the leg belonging to the dog. "Its" is the possessive form of "it," used to indicate that something belongs to a non-human entity. This usage is accurate in the context of the sentence, as the leg that is broken belongs to the dog.

In contrast, the other options contain misspellings or incorrect usages of words that can lead to confusion. The first option uses "deer," which is a type of animal instead of the intended "dear," a term of endearment. The second option mistakenly uses "to" instead of "too," which means excessively. The third option features "there," which indicates a location instead of the correct word "their," which indicates possession (belonging to them). Each of these errors highlights the importance of understanding the meanings and spellings of words to ensure clarity in writing.