The ${\mathrm{pK}}_{{\mathrm{a}}_1}\text{ and }{\mathrm{pK}}_{{\mathrm{a}}_2}$ of an amino acid are 2.3 and 9.7 respectively. The isoelectric point of the amino acid is:

• A

  6.0

• B

  3.7

• C

  12.0

• D

  7.4