The parents waved and _____ the train until it was out of sight.
| A．saw | B．noticed | C．observed | D．watched |
As the boy listened attentively in class, everything his teacher said was easily______.
| A．for him to understand | B．understood | C．to understand | D．to be understood |
Mary is said _____ in the supermarket for 5 years, but I don’t know why she resigned last month.
| A．to have been working | B．work | C．to be working | D．to have worked |
______ from the space, you will find the earth is blue.
| A．Seen | B．Seeing | C．See | D．To see |
He was about to go out for a walk _____ his teacher came to visit him.
| A．while | B．which | C．when | D．then |
I will never forget ____ to country village to see the poor children of my age.
| A．to take | B．to be taken | C．taking | D．being taken |