Think of loose housing as the opposite of the old tie stall barn. In a tie stall or conventional barn, each cow has its own fixed stall where it is tied, fed and milked, all in one spot, in the same building.
Loose housing breaks that fixed arrangement apart. Cows roam freely through a common yard, which can be roofed fully or just partly, resting and feeding wherever they like instead of a fixed stall. Because there is no fixed milking spot at each stall anymore, a separate milking parlour is built where cows are brought in only for milking and then let back into the yard.
This lack of fixed individual stalls also means the barn is not locked into a set number of animals. Adding a few more cows or removing some does not require rebuilding stalls, so herd size can change without much difficulty.
Putting it together, separate milking parlour, free movement in a covered or partly covered yard, and flexible herd size are all true of loose housing. Housing and milking in the same building is the trait of the older tied system, not loose housing, so that statement does not fit.
\[\boxed{\text{Option 4: (A), (B) and (D) only}}\]