21. Post-ranslational modifications are critical for the regulation of biological processes. Which of the followings are the examples of post-translational modifications of proteins? 1) activation of pro-caspase 3 to caspase 3 2) converting PIP2 to PIP3 by PI3 kinase 3) activation of protein kinase A by cAMP 4) activating NF-kb through Ikb kinase 5) epigenetic regulation by histone codes (A) 1,3,4,5 (B) 1,2,4,5 (C)1,4, 5 (D) 2,3,4 (E) All of the above