Stem cells may prove useful in the treatment of type 1 diabetes because
a) they form enzymes that remove excess glucose from the body.
b) they the body to breakdown glucose into a simpler form.
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c) they can be differentiated to form insulin-producing cells.
d) they can be differentiated into cells that can be used to make a new liver.

The answer is C) they can be differentiated to form insulin-producing cells. 

Diabetes is characterized by high blood sugar level. In normal condition, insulin secreted from pancreas maintain blood sugar level by decreasing it. In Type 1 diabetes beta cells of a pancreas which produce insulin are destroyed. Thus, if there is no enough insulin, the level of sugar in the blood remains high. Therefore, stem cells can be used as precursors of pancreatic cells in order to differentiate into insulin-producing cells. This would provide enough insulin to maintain blood sugar level.