PLEASE HELP! What type of reaction is the following?

3fe+4h2o=fe3o4+4h2

A. Synthesis
B. Decomposition
C. Single Replacement/Single Displacement reaction
D. Double Replacement/Double Displacement reaction

Two models of the same compound are shown. in what way is model b better than model a? model b shows the types of elements in the compound, but model a does not. model b shows the three-dimensional shape of the molecule, but model a does not. model b shows how the atoms in the molecule are connected, but model a does not. model b shows the number of atoms of each element in the molecule, but model a does not