a set of keys后加is。a set of keys意为”一串钥匙“，作主语时谓语动词用单数形式is。不能用are。例如：A set of keys is on the desk。桌子上有一串钥匙。
a set of keys后加is还是are
加is
set of keys 一串钥匙;一副钥匙;一套钥匙
As it happens, I have a spare set of keys in my office. 碰巧我在办公室有一套备用钥匙。
My mom gave me a set of keys. 我妈妈给了我一串钥匙。
A set of keys is on the desk. 有串钥匙在桌子上。
Stranger: Excuse me, did you see a set of keys? 陌生人：你好，你看到一串钥匙了吗?