To determine the closest relative of species 4 based on a phylogenetic tree, you typically look for the species that shares a more recent common ancestor with species 4. Without the specific phylogeny mentioned above, I can't provide a definitive answer. However, if species 4 branches directly off from the same node as species 5, then species 5 would be the closest relative. If species 4 shares a node with species 3, then species 3 would be closer. If species 4 shares nodes with both species 1 and 3, then it would be ambiguous, leading to the option “1 or 3 (Can't tell).”
If you can provide specific details or a description of the phylogeny, I'd be happy to help you deduce the correct answer!