A developer created an email using the fasubjectLine variable as the subject line.

When the subjectLine variable is declared in multiple locations throughout the email, the value used at the time of deployment will be the last value assigned to the variable. In the provided declarations, the last assignment is:

%%[ SET @subjectLine = 'Enjoy 20% off today' ]%% was declared within the Subject Line

Therefore, the subject line used at the time of deployment will be "Enjoy 20% off today" (C).