要使海洋生物资源可持续利用，就必须保持海洋生态系统的动态平衡。对一个平衡的生态系统来说，下列叙述错误的是(     )

    Jenny is Mr. White's little daughter. She is good at Art . But she isn't good at Math. Mr. White is teaching her ,”What's six plus three?”

    Jenny counts her fingers and answers ,”It's nine .”

    “Good .What's twenty minus three?”

    Anna counts her fingers and toes. “Mm.it's five .No , it's seventeen .”Jenny answers slowly.

    “What's eleven plus twelve, then ?”Jenny looks at her fingers and toes . They are not enough (足够). Seeing this , Mr. White isn't glad and says, “Use your head, Jenny .”

    “That's not enough .I've got only one head.”

根据短文内容，判断下列句子是否正确。