正确的答案是 c.unless properly managed
句子的完整形式是
Adam is fully aware that unless it is properly managed,his factory will have to close down in less than a year.
句中的 it is 被省略了 （这种省略很正常）.
unless it is properly managed 的意思是 “除非（被）管理得很好”
整个句子是说
亚当非常明白,除非管理得当,他的工厂将不得不在一年之内关闭.