TASK DEFINITION: In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
PROBLEM: Cygnus X-1 was the first X-ray source accepted as a black hole .

SOLUTION: Cygnus X-1 ( abbreviated Cyg X-1 ) is a galactic X-ray source in the constellation Cygnus , and the first such source widely accepted to be a black hole .

PROBLEM: The kilogram is the base unit of mass in the International System of Units ( SI ) .

SOLUTION: The kilogram ( also kilogramme ) is the base unit of mass in the metric system , formally the International System of Units ( SI ) , having the unit symbol kg .

PROBLEM: IFK Go ̈ teborg is an association football club which plays in Sweden for Gothenburg .

SOLUTION:
Idrottsfo ̈ reningen Kamraterna Go ̈ teborg ( officially IFK Go ̈ teborg Fotboll ) , commonly known as IFK Go ̈ teborg , IFK ( especially locally ) or simply Go ̈ teborg , is a Swedish professional football club based in Gothenburg .

