The phrase "it is still questionable" is correct and is often used in written English.
It is typically used to express uncertainty or doubt about something. Example: "The effectiveness of this new treatment is still questionable, as there have been conflicting studies on its success rate."
Thus, Ayurved Siriraj™ has removed ATC from its formulae since last year, although it is still questionable whether the formulae really cause toxicity.
It is still questionable whether the scientists can successfully assemble large clusters of neuromorphic chips.
While it is still questionable whether Latrell Sprewell will play in Seattle on Tuesday night when the Knicks take on Patrick Ewing and the SuperSonics, he still figures that he has an important role to play in the game.
It is still questionable how these advanced systems would react with the human driver.
It is still questionable what effective and efficient Gabor feature representations are.
Therefore, it is still questionable whether industry convergence is a general phenomenon that is prevalent across entire industries.
Acknowledging that Turkey's modernising government had taken the most dramatic steps yet to reform the country's penal code, the group said it was still questionable whether the new laws would be implemented.
Despite the changes, it's still questionable whether Xerox has the financial controls necessary to straighten out the mess.
It's an interesting take on gaming sponsorships, but it's still questionable how effective this is for the brand itself.
Microsoft is going to bring SkyDrive to Windows Phone and iOS, too – though it's still questionable if it will ever come to Android, too.
With all that said, it's still questionable whether or not MyVaccs is more of a feature than a product in itself – is keeping track of vaccinations really a big enough problem to solve all on its own?
