Understanding the USSR’s structure as a federation of constituent republics is what this question tests. The Soviet Union was made up of several Soviet Socialist Republics, each with its own government but under central control in Moscow. Armenia was one of these, the Armenian Soviet Socialist Republic, part of the USSR from 1922 until 1991. The other options—Brazil, Japan, and Canada—are independent countries and were never part of the USSR, so they don’t fit.

The Ho Chi Minh Trail began operation as North Vietnam’s overland supply network to support the Viet Cong in the South, moving weapons, food, and personnel through Laos and Cambodia into South Vietnam. This logistical lifeline started around 1959, when North Vietnam began to push supplies along the trail to sustain the insurgency despite growing U.S. involvement. The other years don’t fit because 1955 is too early for the Trail to have been established, while 1963 and 1969 come after it had already begun and evolved into a broader, continuing operation. So, 1959 is the year the Trail first started being used.

Glasnost and perestroika were reforms that reshaped the Soviet Union in the 1980s by opening up political life and restructuring the economy to introduce more freedoms and market-like elements. The leader who championed these changes was Mikhail Gorbachev. Glasnost allowed more open discussion, greater freedom of the press, and less censorship, while perestroika aimed to modernize the economy by introducing limited market mechanisms and reducing some of the party’s control over decisions. Together, these policies reduced the oppressive controls of the previous era and encouraged dialogue with the West, helping reduce Cold War tensions and paving the way for reforms in Eastern Europe that culminated in the end of the Cold War. Other Soviet leaders did not implement these reforms in the same way. Khrushchev did push de-Stalinization and some reforms earlier, but not glasnost and perestroika. Brezhnev’s era was characterized by political stability with limited reform, and Yeltsin rose to prominence after the Soviet Union’s dissolution, pushing reforms in Russia rather than initiating glasnost or perestroika.

The key idea is sovereignty over a country's most valuable resource. In Iran, that resource was oil. Mossadegh moved to take the oil industry out of foreign hands by nationalizing the Anglo-Iranian Oil Company in 1951, placing control and profits directly under Iranian authority.Oil revenue was central to the economy and foreign influence through oil concessions was a major lever for Western powers, so Britain—and later the United States—took action to protect their interests, culminating in intervention to roll back the nationalization. The other sectors—steel, rail, telecom—were not the focal point of this international push. The oil industry is why Western intervention occurred.