Which of the following statements about the import of protein to the nucleus is correct? choose all that apply. a. an nls can be a monopartite or bipartite signal which includes a significant number of basic amino acids. b. gtp is required for an importin to bind to an nls of a protein destined to be localized to the nucleus. c. ribosomal proteins must display an nls to be localized to the nucleus, and an nes to be localized to the nucleolus. d. the recycling of importins back to their original conformation requires gtp hydrolysis in the cytoplasm.