English multiple choice questions:

The grammar is correct. You can also use a, which means don't run fast. But notice that B is an imperative sentence, and the imperative sentence itself has a imperative mood to express your views on what is happening now. However, No V-ing is mostly used for signs and slogans, making suggestions on things that have not happened yet, and reminding information recipients not to do so. Lack of tone to stop what is happening now. The above is the difference in tone. We need to see that the title runs so fast, and there is such a sentence in it that something is happening. Generally, there is NO ambiguous modifier like so in no V-ing, and it is no problem if no runs fast alone. The questioner skillfully added a so to the stem of the question, indicating that the fact is happening, so he chose B.