Which of the following statements are correct about an ArrayList collection that implements the IEnumerable interface?

1. The ArrayList class contains an inner class that implements the IEnumerator interface.
2. An ArrayList Collection cannot be accessed simultaneously by different threads.
3. The inner class of ArrayList can access ArrayList class's members.
4. To access members of ArrayList from the inner class, it is necessary to pass ArrayList class's reference to it.
5. Enumerator's of ArrayList Collection can manipulate the array.

How many enumerators will exist if four threads are simultaneously working on an ArrayList object?

In which of the following collections is the Input/Output index-based?

1. Stack
2. Queue
3. BitArray
4. ArrayList
5. HashTable

In which of the following collections is the Input/Output based on a key?

1. Map
2. Stack
3. BitArray
4. HashTable
5. SortedList

In a HashTable Key cannot be null, but Value can be.