水泥中掺入石膏，可调节水泥凝结硬化的速度。但也不能掺过多，一般掺量约占水泥重量的()。

A. The light to which the shrimps are sensitive is not the sort of light that the geysers emit.
B. The light given off by the geysers too faint to be detected by the human eye.
C. The heat inside a geyser"s stream is sufficient to kill instantly any bacteria that move into it.
D. Most other types of shrimp use eyes located at the end of eyestalks in order to see.
E. In other types of shrimp a heat-sensing organ has developed that could serve the same geyser-detecting purposes as the light sensitive patches are said to serve.