The correct answer is D) they build platforms based on single issues.
The main criticism of campaigns for third party candidates in the United States elections is that they build platforms based on single issues.
The problem with political campaigns for third party candidates is that they often focus on their own agendas, not in the many or collective proposals to help the many issues the government needs to attend and resolve for all its citizens. That is why they receive so many critics because they only have a single important issue that is its “flag topic” or “key issue” in the campaign.