Which of the following statements are true?

Virtual memory reduces the cost of a context switch.

Virtual memory does a translation from a program's addresses to physical addresses.

Virtual memory allows a process to have an address space in excess of the size of physical memory.

Virtual memory increases the degree of multiprogramming.

a$.2,3,$ and $4.$

b$.1$ and $3.$

c$.1,2,3,$ and $4.$

d$.2$ and $4.$