A:What do you think has happened to Tom
B:What do you think Tom has happened
C:Do you think what has happened to Tom
D:Do you think what Tom has happened
写出下列单词的对应词。
① new ____
② tall ____
③ big ____
水溶性染色剂(PI)能与核酸结合而使细胞核着色,可将其应用于细胞死活的鉴别。将细胞浸泡于一定浓度的PI中,仅有死亡的细胞核会被染色,活细胞则不着色,但将PI注射到活细胞中,则细胞核会着色。利用PI鉴别细胞死活的基本原理是( )