Comments on D-Brane and $SO(2N)$ Enhanced Symmetry in Type II String
  We propose a configuration of D-branes welded by analogous orbifold operation to be responsible for the enhancement of $SO(2N)$ gauge symmetry in type II string compactified on the $D_n$-type singular limit of K3. Evidences are discussed from the $D_n$-type ALE and D-manifold point of view. A subtlety regarding the ability of seeing the enhanced $SO(2N)$ gauge symmetry perturbatively is briefly addressed. 
H. B. Gao