(A):"a series of" (一系列的)前面的谓语动词是用单数;
"There is a series of accidents." 正确.["a" 的前面是不可能用"are"的!]
注:
"a series of", "a set of"一套, "a portion of", "a chain of" ...要用单数形式 "is/was/has been...".
(B):"a series of" 后可加复数名词,不可数名词.