What are the two main distinctions between the east siberian greenish warbler and the west siberian greenish warbler

The two main distinctions between East Siberian greenish warbler and West Siberian greenish warbler is; 1. Their plumage patterns.

2. The wing bars which are used for communication.

West Siberian greenish warblers have a botanical name which they are referred as P. t. viridanus while East Siberian greenish warblers their botanical name is P. t. Plumbeitarsus. Plumbeitarsus have two wing bars while viridanus have one wing bar.

Their southern ring gradually changes the plumage patterns. The male greenish warblers are very good in singing to defend their territories and also to attract female ones.  

the answer is d. none of the above