Such insurers may invest in collateral trust bonds or notes, secured by any of the following: (

a) A deposit of obligations authorized for investment by this

article or Articles 4, 5, or of this

chapter having a market value at least fifteen per cent in excess of the par value of the collateral trust bonds or notes issued. (

b) A deposit of obligations authorized for investment by this

article or Articles 4, 5, or of this chapter, together with other securities, the combined market value of the deposit being at least twenty per cent in excess of the par value of the collateral trust bonds or notes issued, with the par value of the collateral trust bonds or notes not exceeding the market value of the deposited obligations which are authorized for investment by this

article or Articles 4, 5, or of this chapter. (

c) A deposit of obligations authorized for investment by this article, or Articles 4, 5, or of this chapter, together with other securities, and conforming to the following requirements:

(1) The combined market value of the deposit is at least thirty per cent in excess of the par value of the collateral trust bonds or notes issued.

(2) The par value of such collateral trust bonds or notes issued does not exceed the market value of deposited obligations authorized for investment by this article.

(3) The deposited collateral consists of obligations authorized for investment by this article, or Articles 4, 5, or of this chapter, having a market value of at least seventy-five per cent of the par value of such collateral trust bonds or notes issued.