Which of the following statements regarding the Preamble of the Indian Constitution is correct?

I. The Preamble is considered part of the Constitution but is not legally enforceable.

II. The word `Socialist` and `Secular` were added to the Preamble by the 44th Amendment Act, 1978.

III. The Supreme Court in the Kesavananda Bharati case (1973) held that the Preamble is a part of the Constitution.