Dear Sukant2010 and deepak824,
If you change "begun" to "has began" or "began", the sentence ends up having two verbs (has began/began, has been unsuccessful) without a conjunction in between -- not allowed.
The participle form of the verb can act as an adjective modifier qualifying the "attempt". The resulting sentence (A) has one subject (attempt) and one verb (has been unsuccessful). So you do actually need the participle form here.
--Prasad
If you change "begun" to "has began" or "began", the sentence ends up having two verbs (has began/began, has been unsuccessful) without a conjunction in between -- not allowed.
The participle form of the verb can act as an adjective modifier qualifying the "attempt". The resulting sentence (A) has one subject (attempt) and one verb (has been unsuccessful). So you do actually need the participle form here.
--Prasad
