题目解析:
本题为事实信息题,根据题干中的“fortunate”我们定位至本段的第二句话,而题干问的是“why”,那么原因一定就在下文中。接着往下看,“For several generations, the princes of Moscow had the advantage of male succession without interruption or conflict.”这句话就是原因所在,解释了幸运的原因,是因为得益于男性继承权,几代莫斯科王子都在继承王位时避免了纷扰和斗争。所以A选项完全符合文意,故为正确答案。
B选项错误,因为文中没有提到皇室侄子之间相互争夺权力的信息,排除。
C选项错误,因为文中说“In particular, for a long time the sons of the princes of Moscow were lucky not to have uncles competing for the Muscovite seat.”文章提到没有叔叔与皇子们争夺王位,但并没有提到莫斯科王子们愿意与叔叔分享权力,故排除。
D选项错误,选项中说子承父业的继承方式“was relaxed considerably”,但事实上并没有放宽这种继承方式,因为文章中说“direct succession from father to son possessed sufficient standing and support in the principality of Moscow to overcome the challenge”说明这种继承方式在莫斯科获得了足够的支持,故D选项与原文矛盾,排除。