Which is the FOURTH sentence of the paragraph?

Rearrange the following six sentences a, b, c, d, e and f in the proper sequence to form a meaningful paragraph; then answer the questions given below them.
a) On my first day in the city, my local guide Monica Brieskorn walks me down a staircase, below the majestic Dom Cathedral with its towering spires, into an underground car park.
b) I am bewitched by this slice of history, alongside a modern car park! “This was much before a protection law was framed about digging in the city,” she adds.
c) “These are the old Roman foundations and walls of the gate, made of limestone and mortar, that were discovered during excavations,” she explains.
d) In Cologne, Germany, tread carefully, for history may lie, just below your feet.
e) Now, archaeologists would have to be called in, to excavate before construction continues in the city.
f) As I wonder why I am there, she points to a decrepit wall bordering on one side.