Jack is a careless boy. He doesn't write as ------as Mary. A

Cas carefully as 和。。一样认真more的出现无非是混淆视听它想表达：Jack 比 Mary 更认真但是我们看原句,Jack is a careless boy,后面Mary的出现肯定是起对比作用（Mary 更认真）那么那个空肯定就不能填 as more carefully as Mary 了（他没有比Mary认真,也不能说明他比Mary不认真。）还是要根据语境分析