when did i become a citizen???

[kumakuma]

hi all
this is one of those piddly questions that i just can't be sure about. on the "application to sponsor and undertaking" #10 says "are you a canadian citizen?" i say yes, then it asks when i became a citizen. since i was born a citizen, i.e. i'm not naturalized, do i write my birthday or leave it blank?
it can be inferred that i was born a citizen by the next question, but it's not explicit.

 

[ariell]

You are a citizen by birth. Put your birthdate as the date you became a citizen.