Articles - a, an, the (Упражнения)

Elementary (A1)
☆ a/an: 1, 2
☆ a/an, the: 1, 2, 3
☆ a/an, the, no article: 1, 2

Pre-Intermediate (A2)
☆ a/an, the, no article: 1, 2,

Intermediate (B1)
☆ a/an, the: 1
☆ a/an, the, no article: 2
☆ a/an, the, no article with geographical names: 1

Upper-Intermediate (B2)
☆ a/an, the, no article: 1, 2