With the exception of option A, all sentences are written in imperatives (verb structure used for instructions and/or oders) Therefore, in these examples, the call to action is explicit, not implicit. Your best answer is option A because, apart from the fact that it's the only viable one, here you have a persuasive example by consensus. Simply put, instead of telling you directly to do something, it's telling you that everyone is doing it, which is likely to make you want to do it if you want to be like them.