l两道语法 请大家指点

zhengzheng1026UID: 168914

新东方黄皮书 练习１０
３５题 (After) the Boston Tea party in 1773,coffeehouses in the North American colonies (became) centers for gossip,(gamble ),and( political) criticism.
答案是C　gossip 和gamble都是名词　　是不是都应该加“s”?? >>for gossips gambles and political criticism??

新东方黄皮书 练习２０
37题　Wampum,beads used as (a form )of exchange (by )some native Americans,was made of (bits of) seashells cut (drill )and strung into belts.
答案是D 怎么改呢？
有两点不明白（１）为什么是 was made 主语不是 Wampum,beads　？该是were made??
　　　　　　（２）该是　to cut drill and ……. cut drill strung 在这里是什么词性呢？？

请大家指点　谢～～～

avexUID: 159089

35 gambling（名词意思上的区别）
37 drilled

阿奴比斯UID: 2144500

（１）为什么是 was made 主语不是 Wampum,beads　？该是were made??

答:beads used as (a form )of exchange (by )some native Americans这个是定语从句啊