Can you explain ________ the sun goes down in the west?
| A．why is it that | B．why it is that | C．how it is that | D．how is it that |
___ in very good spirits, he worked harder than before.
| A．have built | B．to build | C．to be built | D．to have been built |
The museum ___ at the corner of the street was built in 1879.
| A．stood | B．stand | C．stands | D．standing |
He objected to __ like a child.
| A．be treated | B．being treated | C．treating | D．have been treated |
He found his __ dog yesterday.
| A．losing | B．losed | C．to be lost | D．lost |
The speaker tried hard to make the people ___ him better.
| A．understand | B．understood | C．understanding | D．to understand |