A customer calls in and asks you to help troubleshoot his mobile phone, but he is using the phone that needs troubleshooting. Which of the following is the best thing to say to him?
a) "Please call back on a different phone so we can troubleshoot together."
b) "I cannot assist you while you're using the device."
c) "Try restarting your phone and then call us back."
d) "Can you access a different phone to continue this call?"