thanks. I also read that at IRS website, so many rules.

"The third test is the joint return test. Generally, you are not allowed to claim a person as a dependent if he or she files a joint return. However, you may claim a person who filed a joint return merely to claim a refund of tax. This exception applies if neither the person nor the person's spouse is required to file a return and no tax liability would have existed for either the person or the person's spouse if each had filed a separate return."
above test is so confusing. I am trying to optimize our tax return in all means.