1 a[0] is a t020 and also not null. 2 a[1] is a t020 and also a k and also not null. 3 a[2] is a t020 and also null. 4 a[3] is a t020 and also null. 5 6 Assigning a[0] to u failed. 7 Assigning a[1] to u worked ok. 8 Assigning a[2] to u worked ok. 9 Assigning a[3] to u worked ok.