can't give decarboxylation while normally $\alpha-\beta$ unsaturated acid give this reaction because

• A

  t-butyl gp. has large size and does not let the $\mathrm{COOH}$ group to leave.
• B

  t-butyl gp. can't extract $\mathrm{H}$ from $\mathrm{COOH}$.
• Correct answer
  C

  t-butyl gp. stabilise carbanion formed.
• D

  t-butyl gp. does not allow this composition to convert to $\beta$ - $\gamma$-unsaturated acid

Hence, the correct answer is option: 'C'.