
Take first two pairs
x logx
Let logx = a
So (1/x)dx = da
⇒ dx = xda
Putting the assumed value the equation is reduced to

Now x cancels out so
⇒ 
Again repeat above procedure and keep doing until this equation reduced to 1 term only i.e
Some

Where p = (log(log(log(log)…r times)))
So integration will give logp
So now putting the value answer is
Log(log(log(log(log)))) r+1 times
So answer is lr+1
Correct option is (a)