Consider the inverting amplifier, using an ideal operational amplifier shown in the figure. The designer wishes to realize the input resistance seen by the small-signal source to be as large as possible, while keeping the voltage gain between -10 and -25. The upper limit on `R_F` is 1 M`Omega.` The value of `R_1` should be

Infinity
1 M`Omega`
100 k`Omega`
40 k`Omega`