Unable to tell whether someone really objects to behavioral ads or whether they are sticking with Microsoft's default, some may ignore a DNT( do not track ) signal and press on anyway.

请问老师，

1.开头的unable to tell ... 是形容词从句作状语吗？

2.怎么理解形容词从句作状语？是看作(because we are) unable to tell ... 的省略吗？

3.所有形容词性短语都可以这么用吗？是常态还是个例？