প্রশ্ন: Not until exhaustive tests have been carried out ___.
(ক) that a new drug is allowed
(খ) is a new drug allowed
(গ) there is a new drug
(ঘ) a new drug is allowed
ব্যাখ্যা:
Rule: ‘Not until’ শুরু হলে main clause-এ inversion হয় → auxiliary + subject। Passive হলেও একই rule প্রযোজ্য।