question number 34.

Dear Student,
Mobility of charge μ, responsible of current is defined as the magnitude of drift velocity of charge per unit electric field applied i.e.
                                            μ = v_​d/E
So, if electric field gets doubled the mobility reduced to half.
                                          μ = v_d/2E
Hence, mobility of the electrons depend on the applied electric field. 
Now, 
As temperature increases relaxation time decreases
we have  ,$\mu =\frac{e\tau }{m} \left(e= charge, \tau =relaxation time, m=mass\right)$$\mu =\frac{e\tau }{m} \left(e= charge, \tau =relaxation time, m=mass\right)$
mobility is directly proportional to relaxation time. Relaxation time decreases hence mobility decreases.
Hence, mobility of the electrons also depend on the temperature. 
Therefore, option c is correct. 
Regards