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toalsohaveheartproblems一些医生认为有剔牙习惯的碰巧有心脏问题，故是发展以前的观点，因此选D项。3段落大意题。根据最后一段提到剔牙能保持你的心脏健康这一理论可能并不正确的，但医生同意剔牙能保证牙齿的健康，因此即使剔牙不能有助于你的心脏，肯定能保护你牙齿，这就是每天剔牙的重要原因，故选D项。4主旨标题题。本文提到经过研究，剔牙与保持心脏之间没有必然的联系，但剔牙能保护牙齿的健康是可以肯定的，故选C项。
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