Here I have detailed question.
1.My dad earned $4500 in 2011 and my mom was housewife.
2.Can I claim both? Or just my Mom since she doesn't have any income.
3.they both are legal resident and have SSN.
4.They are part year resident in 2011(around 7 month)
Also,

I didn't claim them my dependent on 2010 Tax return.Can I Amend my return and claim them.
In 2010.
1.My parents didn't have any income and legal resident(with SSN)
2.Lived about 6 month in 2010.

You CAn amend the 2010 return to claim your parents.

You CANNOT claim your father for 2011; he made too much income, but you CAN claim your mother.

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