Bird Species from Temperate Regions Must Cope with Relatively Short

Bird species from temperate regions must cope with relatively short breeding seasons. A study examined the relationship between blood testosterone level (ng/ml) and the duration of the egg-laying period (months) in temperate bird species. The following scatterplot displays this relationship, after taking the logarithm of each variable:
Which units should be attached to the correlation r?

A) ng/ml/month
B) log(ng/ml) /log(month)
C) ng/ml
D) No units; correlation is a unitless quantity