'Probably' beneath the second inference bar. As it stands, however, C2 inherits the qualifier 'Probably' from its ultimate source in P2. The simplest way to think of this is to think of C2 as a proposition inferred from three premises: PI, P2 and P3. If the word 'probably' were deleted from P2, then that argument would be deductively valid. As it stands, however, that argument is only inductively forceful.
Note that in carrying out the inference from CI and P3 to C2, we think of that sub-argument just as if it were presented like this:
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