Concept:The sentence contains four words that need to be swapped in pairs to make logical sense.
Explanation:First, understand the meaning of each marked word:
(A) Their – belonging to them (possessive).
(B) Surprise – unexpected event or feeling.
(C) Parents – mother and father.
(D) Clandestine – secret, hidden.
Now, read the original sentence: "We waited for our their to fall asleep to have our surprise meeting in the living room about parents clandestine anniversary party."
The correct meaning should be: wait for our *parents* to sleep, then have a *clandestine* meeting about *their surprise* anniversary party.
Thus, "their" (A) should swap with "parents" (C), and "surprise" (B) should swap with "clandestine" (D).
So the required swaps are A‑C and B‑D, which matches option "B‑D & A‑C".
Answer:Option C (B‑D & A‑C) is correct.