Which of the following words means 'beam' in German?

The word that means 'beam' in German is "Stab." In German, "Stab" can refer to a rod, stick, or bar, which in certain contexts can be understood as a beam, particularly in construction or structural terms. This makes it the most suitable choice when considering the concept of a beam as a long, sturdy piece of material used to support loads.

The other options, while they may have meanings related to various objects, do not directly translate to 'beam.' For example, "Rohr" translates to 'pipe,' "Stecker" means 'plug' or 'connector,' and "Lastenträger" translates to 'load bearer' or 'load carrier,' which is a more complex term that may imply support but is not as straightforward as the meaning of "Stab" in the context of a beam.