____ his principles, he has to be very careful.

With regard to

With regard of

With regard on

None of these

The phrase "with regard to" is used to reference something specific.

So "With regard to his principles, he has to be very careful" is the correct form.

اپنے اصولوں کے حوالے سے اسے بہت محتاط رہنا پڑتا ہے۔