the water of the lake was so ------that it looks like glass?中间是填still还是calm？为什么？

calm
calm主要用于气候、海洋“ 风平浪静的”, 也可指人表示“安静的”、“镇静的”, 如:

The sky is blue, and the sea is calm.
天空碧兰, 海上风平浪静。
Although she was frightened, she answered with a calm voice.
虽然她害怕, 但还是用平静的声音回答。
still 指“没声音的”、“没动静的”, 如:

the still hours before dawn
黎明前的寂静时刻。

still吧

still
calm主要用来指心情、情绪