From the design perspective, how can the torque of a squirrel-cage induction motor be increased?

Correct option is B

​$$T_{\text{st}} = \frac{KE_2^2 R_2}{Z_2^2} \, \text{N-m}$$

$$T_{\text{st}} \propto R_2$$​​​

It is clear from the above relation that increasing the rotor resistance (R₂) will increase the torque.