AWPhillips's Discovery of a Particular Relationship Between Unemployment and Inflation

A.W.Phillips's discovery of a particular relationship between unemployment and inflation for the United Kingdom

A) could not be extended to other countries,despite many researchers' attempts to provide that extension.
B) was quickly extended to other countries by researchers.
C) was extended to only one other country - the United States.
D) was harshly criticized by the American economists Paul Samuelson and Robert Solow on the grounds that Phillips's study was fundamentally flawed.