Which of the following statements about dBi, dBd, dBc are wrong? (Multiple choice)

Which of the following statements about dBi, dBd, dBc are wrong? (Multiple choice)
A . dBi and dBd are the value of test gain (power gain), both are relative values
B. The reference base of dBi is a dipole, and the reference base of dBd is a dipole omnidirectional antenna
C. If antenna A is 12dBd and antenna B is 19dBd, it can be said that A is 2dBc smaller than B
D. dBc is a unit that expresses the relative value of power, which is exactly the same as the calculation method of dB

Answer: BC