Consider 9 functions f1,f2,,f9, all residing in the RISC-V main memory at different addresses. Let each function have its own author, and assume that the authors can't view each others code. All the authors agree to adhere to the RISC-V guidelines for saving/restoring registers to/from stack memory. The following chart describes which function calls which function: For example, the f1 row implies that function f1 calls functions f2 and f3 and the the f2 row implies that function f2 calls functions f4, f5, and f6. Which of these nine functions needs to save/restore the ra register to/from stack memory? Note: f7,f8,f9 having no rows implies they don't call any other function. f4,f5,f7,f8,f9 f1,f2,f3,f6 f2,f3,f6 None of these All 9 functions