The map shows the physical features of Asia.

A map titled Physical Features of Asia. A key shows the Silk Road with a red line, Lowlands in green, Highlands in yellow, Plateaus in orange, Mountains with brown pyramids. A red line begins in east China and travels west above and below the Taklamakan Desert. The Himalayas are south of the red line. The Zagros Mountains are southwest of the red line. The Ural Mountains are north of the red line.

What physical barrier shown on the map was the biggest obstacle to Silk Road trade?

the Black Sea
the Taklamakan Desert
the Pacific Ocean
the Ural Mountains