The correct option is C Be liked by many forever
Options A and C: According to the line "denim is one of the oldest fabrics but will remain eternally young", the phrase 'eternally young' means that jeans would be a favourite of many for an eternity.
The phrase 'eternally young' on its own refers to everlasting youth or 'remaining young always'. But, in the context of this passage, option C is more suitable, i.e., 'be liked by many forever'. Hence C is the correct option and A is incorrect.
Option B: This phrase gives the meaning of 'eternal' alone, it does not state the meaning of the phrase 'eternally young'. Hence B is incorrect.
Option D: This states a feature of the jeans, but it does not give the meaning of 'eternally young'. Hence D is also incorrect.