article: Dear Sally, Please take these things to your brother Bob: his dictionary, pen, notebook, keys, and a baseball. The dictionary is on the bed. The pen is in the pencil case. I put the pencil case on the sofa. The notebook is on the desk. The keys are on the dresser. The baseball is under the bed. Thanks, Grandma
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question: Sally is Bob's   _  .
options: sister aunt mom grandma