The correct option is A It retains more of the original formatting and so tends to look more attractive.
Online surveys can be sent via email, either embedded in the body of the message or as a separate attachment. The advantage of the latter is that it allows the researcher to use more embellishments and formatting to make the survey look attractive, which in turn may improve the response rate. However, some people may have technical difficulties in opening the attachment, or they may be too worried about computer viruses to risk doing so.