问题如下：
which of the following statements about machine learning is incorrect?
选项：
A.Regression problems involve prediction of a quantitative, continuous dependent variable, such as GDP growth or inflation
B.Linear learning methods try to solve regression problems including partial least squares and principal component analysis;
C.non-linear learning methods include penalized regression approaches, such as LASSO and elastic nets. In penalized approaches, a factor is typically added to penalize complexity in the model, which should improve its predictive performance.
D.In some instances, unsupervised learning is first applied to explore a dataset; the outputs of this approach are then used as inputs for supervised learning methods
解释：
D is correct.
选项D描述的情况不属于Regression problems，选项D描述的情况属于clustering problems.
请问D为什么不正确？不是很理解。unsupervised learning找到的规律作为input给supervised learning这里哪里不对了呢
