In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What led to the result that observers in relative motion measure different elapsed times?, Context: In non-relativistic classical mechanics, Newton's concept of "relative, apparent, and common time" can be used in the formulation of a prescription for the synchronization of clocks. Events seen by two different observers in motion relative to each other produce a mathematical concept of time that works sufficiently well for describing the everyday phenomena of most people's experience. In the late nineteenth century, physicists encountered problems with the classical understanding of time, in connection with the behavior of electricity and magnetism. Einstein resolved these problems by invoking a method of synchronizing clocks using the constant, finite speed of light as the maximum signal velocity. This led directly to the result that observers in motion relative to one another measure different elapsed times for the same event.
a method of synchronizing clocks

What controlling entity might the low countries been afraid of?, Context: In 1579 a number of the northern provinces of the Low Countries signed the Union of Utrecht, in which they promised to support each other in their defence against the Spanish army. This was followed in 1581 by the Act of Abjuration, the declaration of independence of the provinces from Philip II.
provinces from Philip II

What did Luther say he was engrossed in?, Context: Martin Luther married Katharina von Bora, one of 12 nuns he had helped escape from the Nimbschen Cistercian convent in April 1523, when he arranged for them to be smuggled out in herring barrels. "Suddenly, and while I was occupied with far different thoughts," he wrote to Wenceslaus Link, "the Lord has plunged me into marriage." At the time of their marriage, Katharina was 26 years old and Luther was 41 years old.
far different thoughts