Subjecting the growing of which plant to a cold treatment stimulates subsequent photoperiodic flowering response?

Which of the following is a long day plant?

Which of the following factors exclusively affects reproduction in seasonal breeders,both plants and animals?

On germination,a seed first produces shoots with leaves,and flowers appear later.
$(A)$ Why do you think this happens?
$(B)$ How is this advantageous to the plant?

The pigment involved in red-far red light interconversion is

The relation of flowering to the lengths of light and dark periods was investigated by two experiments. In one experiment,the plants were subjected to dark periods of various lengths while the light periods were kept at $4$ hours. In the second experiment,plants were kept in dark periods of various lengths while the light periods were kept at $16$ hours. The number of flowers formed in relation to these periods is shown in the table. These results indicate that flowering:

Dark periods (hours)	Flowers formed (Light: $4$ hrs / $16$ hrs)
$8$	$0$ / $0$
$10$	$0$ / $0$
$12$	$4$ / $6$
$14$	$5$ / $7$
$16$	$5$ / $8$