Can we use "this" to refer to several things?
There's a new attachment added to the gun. There's also a monopod with a hinge on the back for increased support and stability. We replaced the old scope with a new one that can see targets at a much greater range. We also replaced the trigger mechanism with an electronic one for greater security. This sums up all the changes we've made to the gun.
I am not sure if we can use "these". I thought about it, but it sounds weird and for some reason "this" sounds better, but it also seems to be grammatically incorrect.