阅读：获取发明创造的细节信息 — 英语词汇题
题目
Read the passage and complete the sentence with one word.
Ben invented a small holder for his phone. He made it from a piece of thick paper and used two buttons to keep the phone in place. The holder was light, so Ben could carry it in his schoolbag.
Ben used two ______ to keep the phone in place.