Final answer:
Deoxyribose is the sugar that is not readily made from formaldehyde in experiments simulating conditions on primitive Earth.
Step-by-step explanation:
The sugar that is not readily made from formaldehyde in experiments simulating conditions on primitive Earth is deoxyribose. Deoxyribose is a 5-carbon sugar that is a component of DNA. It differs from ribose, which is readily made from formaldehyde, by the absence of an oxygen atom at the 2' position. This difference makes deoxyribose less likely to form under primitive Earth conditions.