Step 1: Idea:
Sort the events into broad periods first: before the Mauryas, the Maurya time, and after the Mauryas.
Step 2: Broad periods:
Buddha lived in the 6th century BCE, which is before all the other events. The Gupta Empire came in the 4th century CE, which is after all the others. So B must be first and D must be last.
Step 3: The middle two:
Alexander crossed the Indus in 326 BCE. Chandragupta Maurya took the throne about 321 BCE. Alexander came first by a few years, so the strict order is B, C, A, D.
Step 4: Use the options:
Only options 3 and 4 begin with B. Option 3 ends with C, which puts Alexander after the Guptas, and that is wrong. Option 4 ends with D and keeps only A and C swapped. So option 4 is the best fit among those given.
Final Answer:
Choose option 4, the closest match.
\[ \boxed{\text{(B), (A), (C), (D)}} \]