In a within-subjects study that extends over a relatively long time, it is possible that there will be systematic changes in the participants’ skills or knowledge during the time of the study. When these changes influence the participants’ scores, causing scores at the end of the study to be different from scores at the beginning, the effect is called .A) a history effect.
B) instrumentation.
C) maturation.
D) regression toward the mean.

A) a history effect.          

Explanation:

History effect: In psychological research, the term "history effect" is described as different events that generally occurs in the specific environment which is responsible for changing the pre-existing conditions of a particular study, therefore affecting or hindering its outcome. However, these history events can occur either between post-test &pre-test or before starting a specific experiment.

In the question above, the given statement signifies a history effect.

ever since wwii tmthey always did hated each other.

the arab empire adopted the muslim religion as their main belief. arabs would influence the people from the territories they invaded towards islam (the muslim belief).

nevertheless, throughout the history of the arab empire, rulers brought intellectual individuals from other religions to their centers of learning. these other foreigners included jews, christians, greeks, persians, and indians.   these resulted in the adoption of important knowledge developed by these cultures by the arabic empire. for example, the works of aristotle were translated from greek to arab and indian scientists brought the numerical concept of "zero" to the arabs.

nowadays, 93% of the arab population is muslim, which at the same time is subdivided in sects including the sunni, zaini, alawi, shia. the remaining 7% is composed mainly of christians.