I can't MeshTrim (Rhino 6 Mac)

Good evening. I want to meshtrim the 4 mesh surfaces alongside the “box” by subtracting them to the horizontal terrain. Both the terrain and the 4 meshes around touch, so they should trim. I want to keep the down part of the 4 meshes, trimming the upper part. I have this due tomorrow for a college project and I’m beyond desperate, any help is welcomeagora a serio.3dm|attachment (10.4 MB)