Hyphens, En Dashes, Em Dashes

Q. Can an em dash be used to connect two complete sentences? For example: “You don’t need to go to the DMV in person to renew your driver’s license—you can renew it online.” Thank you in advance for your answer!

Q. Our typesetter applied Chicago’s never-add-a-hyphen-to-a-URL-breaking-over-two-lines rule to hashtags breaking over two lines (specifically “#MeToo”), and the proofreader marked to force them all to one line, which may result in a lot of loose/tight lines since this occurs quite frequently. Would you suggest stetting the original, going with the proofreader’s fix, or hyphenating?

Q. Do you hyphenate “student teacher”?

Q. Does the Manual defend “on a case-by-case basis” over “case by case”?

Q. I know that the CMOS preference is not to hyphenate “noun + gerund” compounds, but in the case of “decision-making,” which appears with the hyphen in many dictionaries, would CMOS call for a hyphen? Thank you in advance!

Q. When referring to year ranges, I have an author who insists on using “during 1940–45.” I’ve seen “from 1940 to 1945” and “between 1940 and 1945” and simply “1940–45,” but other prepositions sound awkward in this context. To me, something happens during an argument, the winter, the ’80s, an era. That is, something that has a beginning and an end but where those time points aren’t explicitly stated. I would love to hear your thoughts on the matter!

Q. Is the hyphenation in the following sentence incorrect, or is it just not Chicago style? “He had only two seasons with twenty-or-more homers.” Thanks for another great year of Q&A!

Q. In your hyphenation table (CMOS 7.89), why is “mid-twentieth” in “mid-twentieth century” hyphenated? Shouldn’t it be closed up as “midtwentieth century” or have an en dash instead of a hyphen?

Q. Do you recommend using en dashes and em dashes in tweets? Or hyphens?

Q. What is correct style: “X and Y axes” or “X- and Y-axes”?