The red node represent a speciation event and the common ancestor of the species B and C i.e option 1 and 4 are the right answers.
Explanation:
Speciation is an event that leads to splitting in a lineage producing two or more species. The speciation would lead to different species as they no longer can interbreed and produce viable offspring.
The node shows that the two species originated from the same root but undergone speciation to be two different species.
The speciation takes place due to genetic drift, selective breeding and mutations in the population which lead to Natural selection.
In the given picture the root with trait one got modified into trait 4 and 5 via trait 3. This means that due to mutation the genes have changed and evolved for better functions and thus they survived via Natural Selection.
The figure represents diverge population as two new species are there and thus is Allopatric Speciation and have common ancestors.