The use of cell-based models to understand or treat human disease processes is aided by stem cells in all the following ways,except:

A)growth of neurons in cell culture containing mutations associated with ALS for drug screening.
B)culture of patient-specific cells to replace those lost to disease,such as for type 2 diabetes.
C)differentiation of neurons from iPS cells to replace those damaged by neurodegenerative diseases.
D)provides proof that ES cells are pluripotent and can divide to make a normal animal.