The phrase "be sure whether the" is correct and usable in written English.
It can be used when you want to emphasize the importance of confirming or verifying a specific condition or situation.
Example: "Before making a decision, be sure whether the information you received is accurate."
Alternatives: "ensure if the" or "confirm whether the".
Officials said they could not be sure whether the New Jersey infestation portended a wider spread.
As with all posthumous printing, you can never be sure whether the photographer would have approved.
This could explain why those subjects were more prone to addiction but the scientists cannot be sure whether the enlargement is a result of cocaine use.
Because monthly data for December won't be available until next year, we cannot be sure whether the economy has turned down.
Nobody can be sure whether the prime minister will come away from these negotiations with a better deal than he has now.
We cannot be sure whether the chickens and the fish will care, but for us, the humans, these standards are key to avoiding tyrannical behavior.
How are news organisations to know if they are at risk of prejudicing a trial when they cannot be sure whether the defendant has been arrested?
It is hard to be sure whether the gender imbalance shows the resilience of male interest in sex or the resilience of their propensity to boast about it.
My favourite device of all is Stephen R Donaldson's in the Thomas Covenant series, where the reader (and protagonist) can't be sure whether the strange magical universe exists only inside the hero's own head.
But the researchers said that they could not be sure whether the patients' use of anti-inflammatory drugs was a cause of kidney disease, or an effect of it.
But though investigators no longer can be sure whether the youths raped the jogger, few of those reviewing the case question whether the teenagers were involved in the other crimes.
