69. Which of the following statements about membrane proteins are correct? ① Membrane proteins can be extracted from cell membrane using sodium dodecyl sulfate. ② Integral proteins can span the membrane with α-helical structure or β-sheet structure. ③ Estrogen receptor is a membrane protein. ④ The membrane proteins are not associated with membrane through glycosylphosphatidylinositol anchor. ⑤ The transmembrane helix of membrane proteins can be predicted from hydropathic index of amino acid sequence. (A) ①②③ (B) ①②⑤ (C) ①②④ (D) ②④⑤ (E) ①③④