Scientists sometimes make discoveries that lead to a need for new laws. This illustrates the general situation of science not just biology in pursuing scientific inquiry. Some of the classical experiments like the Mendel's crosses of the pea plant to understand the inheritance pattern of various observed traits required Mendel to come up with a hypothesis turned theory of independent assortment of genes. With substantial experimental trails on pea plants this theory turned into a law due to the increased number of supporting evidence.
The answer is D ) Guard Cells.
Guard cells are like a door, they let somethings in and some things out or think of it like a filter it lets certain things in and out
