Step 1: Idea:
An instrument is a string (Tat) instrument if its sound starts from a vibrating string.
Step 2: Ask the question for each item:
Mridangam: sound comes from a stretched skin hit by hand, so no.
Veena: sound comes from plucked strings, so yes.
Tanpura: sound comes from plucked strings, so yes.
Flute: sound comes from a column of air, so no.
Step 3: Collect the yes answers:
The Tat instruments are B and C only.
Step 4: Match with options:
Options 1 and 2 contain A, which is a drum. Option 3 contains D, which is a wind instrument.
Option 4 has only B and C, so it matches.
Step 5: Quick memory aid:
Veena and Tanpura (also sitar, sarod, violin) are strings. Mridangam, tabla and pakhawaj are drums. Flute and shehnai are wind instruments.
Final Answer:
Option 4 is correct: (B) and (C) only.
\[ \boxed{(B)\text{ and }(C)\text{ only}} \]