Mention the question.

Hello...

I am just giving my perspective over it. May be they will give bonus for it but you can learn something by researching on it. Let's start:-

• Option 1 and option 4 can not be answer you can simply google it.
• Coming to option 3,the covering of the eye ball is not cornea; its mainly sclera. Cornea only covers one-third part. And the reason for it being partially correct is that it has collagen (which is a protein itself) and it does cover some part. {Partially correct}
• Coming to option 2, It has dense collagen. It is Avascular { oxygen dissolved in tears secreted from lacrimal gland(exocrine) provide nutrition to it}. And to seal the deal, it is the most sensitive portion of the eye.{correct in all way}

Hope it helps.

Still I will say I am not a biology expert but after referring many books that's all what I can say.