প্রশ্ন: Not until a student has mastered algebra, ___ the principles of geometry.
(ক) he can begin to understand
(খ) can he begin to understand
(গ) he begins to understand
(ঘ) begins to understand
ব্যাখ্যা:
Rule: ‘Not until’ clause সামনে থাকলে main clause-এ inversion হয়। Auxiliary verb subject-এর আগে আসে। Example: Not until he came did we start.