Step 1: Russian legislature.
The Russian Parliament is called the Federal Assembly, consisting of two houses: the State Duma (lower house) and the Federation Council (upper house).
Step 2: Options analysis.
(A) Diet: Parliament of Japan.
(B) Parliament: General term, not specific.
(C) Duma: Correct — the lower house of Russian Parliament.
(D) Senate: Upper house in some countries, not Russia.
Step 3: Conclusion.
The Parliament of Russia is called the Duma (State Duma).