Final answer:
To conclusively prove the presence of cockroaches, a glue trap should be used as it effectively captures the insects, providing visible evidence of an infestation.
Step-by-step explanation:
To prove that you do have cockroaches, you should: a. use a glue trap. Glue traps are an effective way to monitor and confirm the presence of cockroaches in your home. When placed in areas where cockroaches are suspected to travel or hide, these traps can catch the insects, providing visible evidence of an infestation. Leaving food out or using lights will not conclusively prove the presence of cockroaches, as they can avoid these conditions and remain hidden. Spraying pesticides is a method of control and does not serve as a monitoring tool to prove their existence.