Final answer:
Deoxyribose is the sugar that is not readily made from formaldehyde in experiments simulating conditions on primitive Earth.
Step-by-step explanation:
Sugar, such as glucose, fructose, and ribose, can be made from formaldehyde in experiments simulating conditions on primitive Earth. However, deoxyribose is the sugar that is not readily made from formaldehyde under those conditions.
Deoxyribose is a sugar found in DNA, and it differs from ribose by having one less oxygen atom in its structure. Due to this difference, deoxyribose is not easily formed from formaldehyde in experiments simulating the conditions on primitive Earth.