Which of these is a Russian triangular musical instrument?

Balalaika is a traditional Russian instrument with a wooden triangle-shaped body and three (or rarely six or four) strings. It is sometimes called a “Russian three-string guitar.” It was developed in the 18th century from the dombra, or domra, a round-bodied, long-necked, three-stringed lute played in Russia and Central Asia.

For centuries, balalaika was a popular village folk instrument played by skomorokhs (a kind of jester-musician) to entertain people. The instrument was used in folk music but was also employed in large balalaika orchestras in the 20th century.

Some researchers suppose that the three sides and three strings of the balalaika may symbolize the Holy Trinity. But this theory is rather weak: at different times in Russian history the instrument was banned by the Church and, moreover, musical instruments are not allowed in the Orthodox liturgy.