Susan jones has the following municipal bonds in her portfolio.

$20,000 aaa sacramento muni asst 8% due 7/11
$30,000 aa los angeles, ca go 4.5% due 7/01/15
$50,000 a-1 ca state go 5.24% due 09/01/16
$50,000 a-1 ca state pwr rev 5.9% due 07/15/17
$10,000 a ca state fin. auth (univ) 3.80% due 08/15/25

these bonds have satisfied the requirement of diversification in all of the following ways except?
[a] final maturity dates
[b] the purpose for which the bonds were issued
[c] the quality of the bonds
[d] the issuer of the bonds