Strong basis means that the basis is positive, the value is getting bigger and bigger, or the basis is changing from negative to positive, or the basis is negative, and the absolute value is getting smaller and smaller. Conversely, a weaker basis means that the basis is positive and the value is getting smaller and smaller, or the basis is changing from positive to negative, or the basis is negative and the absolute value is getting bigger and bigger. ABD three items belong to the weak foundation. Therefore, this question chooses C.