Which one of the following pairs is not correctly matched?

Plants which behave as mesophytes in rainy season and as xerophytes in summers are called:

Name a hormone which:
$(A)$ is gaseous in nature
$(B)$ is responsible for phototropism
$(C)$ induces femaleness in flowers of cucumber
$(D)$ is used for killing weeds (dicots)
$(E)$ induces flowering in long day plants

Formative hormone is

$A$ sleep movement in plants is a nastic response that occurs daily in response to

During experimentation, why is it difficult to attribute any observed effect to a single hormone?