In my county, the native plant society is forty-nine years old.
Explanation:
The sentence includes the age of the plant. And the word "forty-nine" is a one word phrase, a compound number that has to be together as they signify the age of the plant. So, the 'hyphen' is used in between 'forty' and 'nine'. While the other sentences' use of the dash (last sentence) or no use of it (second sentence) is wrong. The second use of the hyphen is not required after 'nine'. Thus, the correct answer with the correct punctuation is-
In my county, the native plant society is forty-nine years old.
I think that is “none of these” since a plot is a sequence of event in a story and each causes or lead to the next. Events of the plot reveal a problem called the conflict.
