The sentence that uses dashes correctly is A) I'd love to stay and talk, but - yikes! I'm really late now. Since you introduced an exclamation <em>yikes, </em>you also need to separate it from the rest of the sentence using a dash.
A. <span><span>I'd love to stay and talk, but—yikes! I'm really late now. </span>This is the correct answer. The dash here is used properly because it shows the break in thought, and it changes the tone of the speaker. That is one use of dashes. <span> B. </span></span><span>Today we studied a poem, did an experiment, and multiplied fractions. (The sentence doesn't need the dash.) C. </span><span>The coat—one of the most colorful that I've seen--seemed to be made of string. (It needs another dash after seen.) </span>D. <span>There on the stage was my sister! (Does not need the dash.)</span><span>
