To solve this question, the user needs to be familiar with common naming conventions for controls in user interfaces. Specifically, the user should know the standard prefixes used for button and combo box controls.

Now, let's go through each option and explain why it is right or wrong:

A. btn and chb: This option is incorrect. The prefix "btn" is commonly used for button controls, but the prefix "chb" is not typically used for combo box controls.

B. btn and cbo: This option is correct. The prefix "btn" is commonly used for button controls, and the prefix "cbo" is commonly used for combo box controls.

C. bto and chb: This option is incorrect. Neither the prefix "bto" nor the prefix "chb" are commonly used for button or combo box controls.

D. bto and cbo: This option is incorrect. The prefix "bto" is not commonly used for button controls, and the prefix "cbo" is commonly used for combo box controls.

E. cmd and cbo: This option is incorrect. The prefix "cmd" is not commonly used for button controls, and the prefix "cbo" is commonly used for combo box controls.

The correct answer is:

B. btn and cbo