UK History: Chapter 3, Exercise 2 — Possible Solution
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QUALIFICATION
In 927 Æthelstan conquered York and became the first Anglo-Saxon ruler of all
England, but the source says some scholars dispute calling him the first king
of England, and quotes Charles Insley saying his hegemony was perhaps not
attained again until Edward I, suggesting it was fragile.

REWRITE
"Æthelstan conquered York in 927 and ruled as King of the English until 939;
historians describe him as the first king of England, though some dispute
that and his hegemony may have been fragile."