Although the Expression of Most Genes Is Tightly Regulated, Some

Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates i.e., constitutively) . Which of the following genes would you predict to be constitutively expressed?

A) genes involved in the biosynthesis of the amino acid tryptophan
B) genes involved in the transport of the sugar maltose
C) genes that code for ribosomal RNAs
D) genes involved in the degradation of arabinose, a sugar
E) genes involved in the degradation of tryptophan