Basically，these attitudes amount to a belief ________ leisure can and should be put to good use
B
空格前面是belief，后面是一个结构完整的句子，解释说明belief的具体内容。所以用that引导这个同位语从句。
Thegovernmentfinally________allthedocumentsrelatingtothewar.
Thestudentsarerequiredto________themainideasofthearticleintheirownwords.
Theyshouldtryto________theirusualinhibitionsandjoininthefun.
Thefarmingmethodshavebeen________improvedwiththeinventionofthenewmachine.