Alice: Good morning, Bob. Bob: Good morning, Alice. Alice: Bob, this is Grace. Bob: Hi, Grace. Grace: Hi, Bob. Alice: Oh, what is that? Bob: It's my green key. Alice: What's this? Bob: It is a ruler. Alice: Is it your   ruler? Bob: No. My ruler is red. This ruler is blue. Alice: Grace, is it your ruler? Grace: Oh no. It is Frank's ruler. Alice:40 . The ruler is   _  .
red and blue white and black blue black