正确的是There is a pen,a knife and several books on the desk.
be 动词按下面的原则确定：
(a)当There be 后面的名词是单数名词或不可数名词时,用is.
(b)当There be 后面的名词是复数名词时,用are.
(c)当There be 后面的名词是用and连接的两个或多个名词时,be【就近一致】,即离哪一个名词近,就随那个名词变化.
如 There is a table in the room./ There are some people under the tree./ There is much water on the floor./ There is a pen,two pencils and many books on the desk.