Test and analysis: because the calm water surface is equivalent to a flat mirror, the reflection of trees on the shore of the lake is formed by the reflection of light;
The crystal-clear Lijiang River looks shallower than it really is because light enters people's eyes from the water through the air, so it is a virtual image formed by light refraction.
Comments: This question examines the reflection and refraction of light, which is relatively simple and belongs to common examination questions.