(a) For the class A felony of murder in the second degree, the term shall be life imprisonment;

(b) For the class A felony of arson in the first degree, or for the class A felony of kidnapping in the first degree the term shall be fixed by the court, and shall be at least twelve years but shall not exceed fifteen years;

(c) For a class B felony, the term shall be fixed by the court, and shall not exceed ten years;

(d) For a class C felony, the term shall be fixed by the court, and shall not exceed seven years; and

(e) For a class D felony, the term shall be fixed by the court and shall not exceed four years. 3. Minimum period of imprisonment. The minimum period of imprisonment under an indeterminate sentence for a juvenile offender shall be specified in the sentence as follows:

(a) For the class A felony of murder in the second degree, the minimum period of imprisonment shall be fixed by the court and shall be not less than five years but shall not exceed nine years provided, however, that where the sentence is for an offense specified in subdivision one or two of section 125.25 of this chapter and the defendant was fourteen or fifteen years old at the time of such offense, the minimum period of imprisonment shall be not less than seven and one-half years but shall not exceed fifteen years;

(b) For the class A felony of arson in the first degree, or for the class A felony of kidnapping in the first degree, the minimum period of imprisonment shall be fixed by the court and shall be not less than four years but shall not exceed six years; and

(c) For a class B, C or D felony, the minimum period of imprisonment shall be fixed by the court at one-third of the maximum term imposed.