Which of the following statements is true concerning the use of cyclic di-GMP as a second messenger?

A) It activates the expression of flagellin genes and thus enhances motility.
B) It is found in all microbes: bacteria, archaea, and eukaryotic microbes.
C) The action of diguanylate cyclase produces it.
D) It decreases in level as biofilm is produced.
E) Phosphodiesterase can convert GMP to cyclic di-GMP.