We investigate electronic transport property of a graphene monolayer covered by a graphene nanoribbon. We demonstrate that electronic transmission of a monolayer can be reduced when covered by a nanoribbon. The energy at which the transmission reduction occurs depends on the width of nanoribbon. We explain the transmission reduction as interference between wavefunctions in the monolayer and the nanoribbon. Furthermore, we show that the transmission reduction of a monolayer is combinable when covered by more than one nanoribbon and we propose a concept of "combination of control" for possible nano-application designs.