Final answer:
The precise percentage of NWCR members who weigh themselves weekly is not given; however, since 'most members' do this, the percentage is likely over 50%, suggesting that option D) 70% could be correct.
Step-by-step explanation:
The percentage of individuals in the US National Weight Control Registry (NWCR) who weigh themselves at least once a week is not explicitly stated in the provided information. However, there is an important related detail that can be extracted. According to the details given about the NWCR members, it states that most members weigh themselves at least once per week, which implies that the percentage is over 50%. While the exact percentage is not provided in the options A) 15%, B) 30%, C) 45%, D) 70%, it suggests that the correct answer could be D) 70%, assuming that 'most' hints towards a significant majority.