Question

which challenge did john roebling face when designing and building the brooklyn
roebling had never designed a suspension bridge before.
he did not have enough workers to build the bridge
the suspension bridge would be the longest ever built.

Explanation:

John Roebling had designed suspension bridges before (e.g., the Niagara Falls Suspension Bridge). There is no indication of a lack - of - workers issue. However, the Brooklyn Bridge was intended to be the longest suspension bridge ever built at that time, which was a significant engineering challenge.

Answer:

The suspension bridge would be the longest ever built.