我怡好从美国消费品安全委员会里看到一份文件PDF格式的，上面告诉我们，四岁五岁是孩子“骑儿童自行车”的适当年龄。

I did come across a document (PDF) from the U.S.Consumer Product Safety Commission that suggests that ages four and five are when it's appropriate for kids to "ride small bicycles."

youdao

我怡好从美国消费品安全委员会里看到一份文件(PDF格式的)，上面告诉我们，四岁五岁是孩子“骑儿童自行车”的适当年龄。

I did come across a document (PDF) from the U. s. Consumer Product Safety Commission that suggests that ages four and five are when it's appropriate for kids to "ride small bicycles."

youdao

我怡好从美国消费品安全委员会里看到一份文件(PDF格式的)，上面告诉我们，四岁五岁是孩子“骑儿童自行车”的适当年龄。

I did come across a document (PDF) from the U.S. Consumer Product Safety Commission that suggests that ages four and five are when it's appropriate for kids to "ride small bicycles."

youdao