(a) In order to hasten the completion of the improvement, the commission is authorized to borrow money not exceeding the estimated cost of improvement, including in the cost of the improvement the interest which may accrue upon the bonds which may be issued to raise funds to pay for the improvement, and to issue interest-bearing bonds therefor. The commission may pledge all the uncollected assessment, or so much thereof as may be necessary for the payment therefor, except such assessment as may be required to be pledged for the acquisition of the real estate on which the improvement is to be located and such as may be necessary to create a sinking fund to pay the bonds or to retire them.
(b) The bonds shall be a lien upon the real estate of the district.
(c) The commission shall create a sinking fund from the annual assessments in order that the bonds may be paid at maturity or retired earlier, if possible, or the commission may provide for the annual retirement of a portion of the bonds from the assessment levied.