需要一些SelectMany的帮助

假设我有一个IEnumerable<Tuple<string, object>>，并且我想用(几个)其他元素的列表替换枚举的每个元素的第一个元素:

Original enumerable: { { "a", obj1 }, { "b", obj2 } }
First-element replacement: a -> { "c", "d" }, b -> { "e", "f", "g" }
Result : { { "c", obj1 }, { "d", obj1 }, { "e", obj2 }, { "f" , obj2 }, { "g" , obj2 } }

我怎样才能用比

更好的方法来完成SelectMany呢?

enumerable.SelectMany(item => ReplacementFunction(item.Item1).Select(newItem =>
new Tuple<string, object>(newItem, item.Item2)))

var query = from tuple in enumerable
            from replacement in ReplacementFunction(tuple.Item1)
            select Tuple.Create(replacement, tuple.Item2);