what's that ____ was flsahed in the sky just now?为啥添which?

what's that ____ was flsahed in the sky just now?为啥添which?
what's that ____ was flsahed in the sky just now?
为啥添which?

what's that ____ was flsahed in the sky just now?为啥添which?
这是一个定语从句的特殊疑问方式.which引导的后面的句子是对that 的解释说明.

应该是flashed吧
主句what's that ,
which was flashed in the sky just now 做定语从句修饰that
句子中已经有了that,所以只能用which 来做连接词~

从句

flowerqc
的答得较好
但
“句子中已经有了that,所以只能用which 来做连接词”
我在语法书中没找到依据