Which phytohormone is useful for leaf expansion in leafy vegetables?

In green plants,cell elongation in the internodal regions is caused by which of the following?

Which of the following are effects of gibberellins?
$(a)$ It helps overcome apical dominance.
$(b)$ It delays senescence,thus fruits can be left on the tree longer.
$(c)$ Increase in length of axis.
$(d)$ It is used to speed up the malting process in brewing industries.
$(e)$ It induces parthenocarpy.
$(f)$ Promotes female flowers in cucumbers.

The gibberellins are plant growth hormones. They cause elongation of stems. Gibberellin was first isolated by Japanese workers from

$A$ genetically dwarf plant can be converted into a tall plant by the use of

Dwarfness can be controlled by treating the plant with