The correct option is
A passion
A synonym is a word that means the same as another word.
Option A: 'Zeal' means 'great energy or enthusiasm for a cause or objective'.
'Passion' means 'an intense desire or enthusiasm for something'.
As you can see, 'passion' means the same as 'zeal'. Hence it's the synonym we're looking for and option A is correct.
Option B: 'Crazy' means 'extremely enthusiastic, mad'.
This word is stronger in meaning compared to 'zeal'. Hence this isn't the suitable word.
Option C: 'Allure' means 'being powerfully and mysteriously attractive'.
Option D: 'Alert' means 'quick to see, understand and act in a particular situation'.
These words do not share the same meaning as 'zeal'. Hence options B, C and D are wrong.