→ I is true because when we make a function call there are some input registers and some output registers. If function F() is calling function G(), we can make the caller function F()'s output registers the same as the called procedure G()'s input registers this is done using overlapping register windows.This will reduce the memory accesses so that F()'s output need not be put into memory for G() to access again from memory.
→ II is false as register saves and restores would still be required for each and every variable.
→ III is also false as instruction fetch is not affected by memory access using multiple register windows.