Problem: Please answer a question about the following article about Middle Ages:
The development of a three-field rotation system for planting crops[AA] increased the usage of land from one half in use each year under the old two-field system to two-thirds under the new system, with a consequent increase in production. The development of the heavy plough allowed heavier soils to be farmed more efficiently, aided by the spread of the horse collar, which led to the use of draught horses in place of oxen. Horses are faster than oxen and require less pasture, factors that aided the implementation of the three-field system.
What invention led to an increase in efficiency in the farming of heavy soils?
A: the heavy plough
Problem: Please answer a question about the following article about Sanskrit:
Sheldon Pollock argues that "most observers would agree that, in some crucial way, Sanskrit is dead".:393 Pollock has further argued that, while Sanskrit continued to be used in literary cultures in India, it was never adapted to express the changing forms of subjectivity and sociality as embodied and conceptualised in the modern age.:416 Instead, it was reduced to "reinscription and restatements" of ideas already explored, and any creativity was restricted to hymns and verses.:398 A notable exception are the military references of Nīlakaṇṭha Caturdhara's 17th-century commentary on the Mahābhārata.
What is Sanskrit not  able to express?
A: the modern age
Problem: Please answer a question about the following article about Railway electrification system:
DC commutating electric motors, if fitted with laminated pole pieces, become universal motors because they can also operate on AC; reversing the current in both stator and rotor does not reverse the motor. But the now-standard AC distribution frequencies of 50 and 60 Hz caused difficulties with inductive reactance and eddy current losses. Many railways chose low AC frequencies to overcome these problems. They must be converted from utility power by motor-generators or static inverters at the feeding substations or generated at dedicated traction powerstations.
What problems did AC distribution cause?
A: inductive reactance and eddy current losses
Problem: Please answer a question about the following article about Dissolution of the Soviet Union:
The Baltic Way or Baltic Chain (also Chain of Freedom Estonian: Balti kett, Latvian: Baltijas ceļš, Lithuanian: Baltijos kelias, Russian: Балтийский путь) was a peaceful political demonstration on August 23, 1989. An estimated 2 million people joined hands to form a human chain extending 600 kilometres (370 mi) across Estonia, Latvia and Lithuania, which had been forcibly reincorporated into the Soviet Union in 1944. The colossal demonstration marked the 50th anniversary of the Molotov–Ribbentrop Pact that divided Eastern Europe into spheres of influence and led to the occupation of the Baltic states in 1940.
What states did the chain extend over?
A:
Estonia, Latvia and Lithuania