Which of the following sets is not a natural plant growth regulator?

Opening of a flower and drooping of a bud are examples of

The movement of plant organs in response to light is called:

Both ethylene and $ABA$ are responsible for

Analogy type question:
$(1)$ Initial growth : Lag phase :: Rapid growth : .........
$(2)$ $IAA$ : Indole compounds :: Abscisic acid : .......

Fill in the blanks with appropriate word/words.
$(a)$ $A$ phase of growth which is maximum and fastest is $.......$ .
$(b)$ Apical dominance as expressed in dicotyledonous plants is due to the presence of more $.......$ in the apical bud than in the lateral ones.
$(c)$ In addition to auxin,a $.........$ must be supplied to culture medium to obtain a good callus in plant tissue culture.
$(d)$ $.........$ of a vegetative plants are the sites of photoperiodic perception.