1. (2020·杭州模拟) 某同学在野外观察到五种动物P、Q、R、S和T，并设计如表所示的二歧分类检索表来分辨这些动物。下列有关叙述中，正确的是（    ）

1a身体内无脊椎骨···2

1b身体内有脊椎骨···3

2a水生··················P

2b陆生·················Q

3a 皮肤裸露············R

3b皮肤不裸露·········4

4a用鳃呼吸············S

4b用肺呼吸············T