16.skeptical a. 表示怀疑的

　　例句11.I am rather skeptical about their chance of winning.

　　17.sketch n. 素描，速写，略图；v. 速写，写生

　　例句12.A short, usually descriptive literary sketch. 小品文简洁的描述性文学短文

　　例句13.Sketch out what you intend to do.

　　18.slacka. 不景气的，萧条的

　　例句14.Business is slack now

　　例句15.He is slack in his duties.

　　²slam v. 砰地关上

　　19.slender a. 细长的，苗条的

　　²slim a 苗条的

　　20.slip v. 滑，滑倒； v. 溜走；n. 疏忽，笔误，口误, 收条

　　例句16.Errors will slip in.

　　例句17.Here's the deposit slip.

　　²slipper， n. 拖鞋

　　Slippery，滑的