some language experts think ------- we are born with is a ge

答案是A 这是省略 that的宾语从句 what从句是宾语从句中的主语 从句 what是从句中with的宾语
原句= some language experts think that what_ we are born with is a general ability to learn and adapt, not a language-specific part of the brain.
如果 非选that的 话 应该是
some language experts think that something we are born with is a general ability to learn and adapt, not a language-specific part of the brain.
这里的that是引导宾语从句的连词 也可以省略
sth 是宾从中的主语 we are born with是省略that的定语从句