Final answer:
The illusion is that desserts can be enjoyed in moderation.
Step-by-step explanation:
The illusion and meaning of desserts becoming a forbidden fruit for those on a strict weight loss diet is that desserts can be enjoyed in moderation (b). It is not necessarily true that all desserts are unhealthy (a) or that they have no impact on weight loss (c). Nor is it true that desserts are the only enjoyable food (d).