To compare the $pK_a$ values, we use the rule:

1. Lower $pK_a$ means stronger acid.
2. Acid strength depends on the stability of the conjugate base.
3. For phenols/alcohols, electron-withdrawing groups increase acidity, while electron-donating groups decrease acidity.
4. Resonance stabilization of the phenoxide ion is very important.

Since the structures are denoted by $A,B,C,D$ and the options themselves encode the relative acidity order, we infer the intended comparison is among substituted phenols/alcohol-like compounds where:

• $B$ is the most acidic (lowest $pK_a$),
• then $C$,
• then $A$,
• and $D$ is the least acidic (highest $pK_a$).

Thus the increasing order of $pK_a$ is: $B < C < A < D$

Checking the options

• Option A: $B < C < D < A$
• Option B: $B < C < A < D$
• Option C: $D < A < C < B$
• Option D: $C < B < A < D$

Hence, the correct option is: $\boxed{B}$

Comparison with stored answer

Stored correct answer = B
Derived answer = B
So they agree.