Question:
"_____ the malfunctions of dishwasher are due to defects or low-quality material is still being investigated."
I don't know should I choose "Whether" or "While" to fit into the space. The answer is "While", but I don't see it's a perfect answer, and I don't understand why I cannot use whether. Is it because that both of two reasons (defects and low-quality material) are possible?
Thanks!