Which statement is false?

Check option (a):

In C language, function arguments are passed by value.

It means a copy of the actual argument is passed to the function.

So, option (a) is true.

Check option (b):

Call by reference allows a function to modify the original variable of the calling function.

So, option (b) is true.

Check option (c):

Call by value is not always more efficient than call by reference.

For large data structures, passing by reference or using pointers can be more efficient because copying large data is avoided.

So, option (c) is false.

Check option (d):

C does not directly support call by reference.

But programmers use pointers and indirection operators to simulate call by reference.

So, option (d) is true.

Therefore, the false statement is option (c).