<b>a. I don't think there would be a rule, just an expectation.</b><br/><br/><b>b. I don't think there would be a rule, but just an expectation.</b><br/><br/><b>c. I don't think there would be a rule, only an expectation.</b><br/><br/><b>d. I don't think there would be a rule--just an expectation.</b><br/><br/>Are all the above correct in formal texts? If not, which aren't and why?<br/><br/>Thanks