4. The 3' end of most eukaryotic mRNAs contains a ________ and the 5' end has a ________. (A)poly（Ａ） tail, methylated guanosine cap (B) poly（U） tail, methylated guanosine cap (C) methylated guanosine cap, poly（Ａ） tail (D) poly（Ａ） tail, sulfonated guanosine cap (E) methylated guanosine cap, poly（U） tail