Problem: Does "Feudal levies could only be raised for a fixed length of time before they returned home, forcing an end to a campaign; mercenary forces, often called Brabancons after the Duchy of Brabant but actually recruited from across northern Europe, could operate all year long and provide a commander with more strategic options to pursue a campaign, but cost much more than equivalent feudal forces." answer the question "What castle was built at a strategic point?"

A: no

Problem: Does "These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals, complicating the design of pipelines and storage tanks." answer the question "When are these useful?"

A: yes

Problem: Does "From the early stages of Christianity, belief in the virginity of Mary and the virgin conception of Jesus, as stated in the gospels, holy and supernatural, was used by detractors, both political and religious, as a topic for discussions, debates and writings, specifically aimed to challenge the divinity of Jesus and thus Christians and Christianity alike." answer the question "For what purpose did detractors use the idea of Mary's virginity and the virgin conception of Jesus?"

A:
yes