I'm________about what I say because careless remarks are likely to hurt others' feelings.
A:enthusiastic
B:curious
C:doubtful
D:cautious
①黑×棕→1匹黑 ②黑×黑→2匹黑 ③棕×棕→3匹棕 ④黑×棕→1匹黑+1匹棕
根据上面的结果,下列说法正确的是( )