Your answer is D. Formation of NADPH
I took the test and got the same answer
The correct answer is (b.) an increase in the width of the stem. The increase in the width of the stem could be referred to as the secondary growth of the stem. Whereas the primary growth is the upward growth of the plant.
When stem cells grown on hard, rigid surface, then they became bone cells. Researchers demonstrate in Nature materials that human mesenchymal stem cells grown on a rigid substrate for some time become biased toward differentiating into bone-cell lineage, whereas cell grown on softer surfaces are just likely to eventually follow a bone or fat cell fate.