If you worked only for a very short period in A (1, 2, 3, 4 months), you can hide a gap of above 5 months that may be questioned. Otherwise, I have a few questions for you here:
1. What is the harm in sharing the details?
2. How many years did you work in "A"?
3. Are you prepared with a justification for the duration of your employment at "A" company (1/2/3 years) if you are hiding it?
4. What if "C" asks you to submit all relieving and experience letters from previous employers during onboarding?
Regards,
Piyush
Manager HR - Pune