It is impossible for a baby with blood type O+ to have a mother with:

Human blood groups are inherited from parents based on specific genetic combinations of the ABO system and the Rh factor. Blood type O+ means that a person has:

1. 
   

   Blood group O: No A or B antigens on the surface of red blood cells.

   
   


2. 
   

   Rh positive: Presence of the Rh (D) antigen.

   
   

For a baby to have blood type O, both parents must contribute the O allele (since O is recessive), meaning neither parent can pass on an A or B antigen. A mother with AB blood type always passes on either an A or B gene, never an O gene. Therefore, a baby cannot inherit type O blood from an AB mother.

Breaking down the options:

• 
  

  AB-: This mother’s genes are A and B, so she cannot produce an O baby. This combination is impossible.

  
  


• 
  

  O-: This mother has two O alleles and could easily produce an O baby if the father contributes an O allele. The baby would also likely be Rh positive if the father is Rh+.

  
  


• 
  

  O+: A mother with this type can naturally produce an O+ baby if the father also has an O or compatible type.

  
  

The Rh factor (+ or -) only determines the presence or absence of the Rh antigen and does not affect the ABO inheritance rules. Therefore, the only impossible case is a baby with blood type O+ having a mother with AB- blood type, as genetically this combination cannot produce O offspring.

Thus, the correct answer is AB-.