Silene Is a Genus of Plants in the Caryophyllaceae

Silene is a genus of plants in the Caryophyllaceae.Many species of this plant have separate male and female individuals.Two populations may have evolved reproductive isolation.Which method would best determine if they exhibit temporal isolation?

A) Examine the pollen and ovules of the different populations in the lab. If pollen of one population fertilizes the ovules of the other with high success, then they likely have temporal isolation.
B) Examine the pollen and ovules of the different populations in the lab. If pollen of one population fertilizes the ovules of the other with low success, then they likely have temporal isolation.
C) Examine when each population flowers. If they do so around the same time, then they likely have temporal isolation.
D) Examine when each population flowers. If they do so at different times, then they likely have temporal isolation.
E) Examine the soil type in which individuals from both populations grow best. If the ideal soil type differs, then they have temporal isolation.