new[] { "abc", "abcd;;;;", ";;;ab", "ab;cd;efg;;;" }
                    .Select(x => Regex.Replace(x, ";+$", r => string.Empty))
                    .Aggregate(Console.Out, (a, b) => { a.WriteLine(b); return a; });

 var sArr = new[] { "abc", "abcd;;;;", ";;;ab", "ab;cd;efg;;;" };
                var mArr = string.Concat(sArr);

      [ComVisible(false)]
        public static String Concat<T>(IEnumerable<T> values) {
            if (values == null)
                throw new ArgumentNullException("values");
            Contract.Ensures(Contract.Result<String>() != null);
            Contract.EndContractBlock();

            StringBuilder result = StringBuilderCache.Acquire();
            using(IEnumerator<T> en = values.GetEnumerator()) {
                while (en.MoveNext()) {
                    if (en.Current != null) {
                        // handle the case that the enumeration has null entries
                        // and the case where their ToString() override is broken
                        string value = en.Current.ToString();
                        if (value != null)
                            result.Append(value);
                    }
                }            
            }
            return StringBuilderCache.GetStringAndRelease(result);
        }

 [ComVisible(false)]
        public static String Concat(IEnumerable<String> values) {
            if (values == null)
                throw new ArgumentNullException("values");
            Contract.Ensures(Contract.Result<String>() != null);
            Contract.EndContractBlock();

            StringBuilder result = StringBuilderCache.Acquire();
            using(IEnumerator<String> en = values.GetEnumerator()) {
                while (en.MoveNext()) {
                    if (en.Current != null) {
                        result.Append(en.Current);
                    }
                }            
            }
            return StringBuilderCache.GetStringAndRelease(result);            
        }