IT'S a mystery that has puzzled scientists. Five years ago, researchers found an area in the Atlantic Ocean seabed, where a part of the Earth's outer layer, or crust（地壳）, is  missing. A thick layer of dark green rock, which is usually found deep inside the planet, lies exposed.
The crust, mantle(地幔) and core（地核） are the main layers that make up the planet. The mantle rests between the crust and the core.
Last month, a team of 12 British scientists set off on a six-week trip to study the hole in the crust.
The hole is about 4,800 meters below sea level and is believed to be more than 48,000 meters long and more than 48,000 meters wide. Scientists think that there are other nearby gaps. "It is like a window into the interior (内部) of the Earth," says scientist   Bramley Murton, who is part of the research team.
The site where the hole is located is part of a ridge (山脉) of undersea volcanoes.  There, two of the plates that make up the Earth's surface meet. The plates are always   moving. When the plates move away from each other, lava rushes up from the mantle to   fill the gap and form a new crust. But this did not happen in the area where the hole is located.
The hole is giving researchers a good opportunity to study what's below the Earth's   surface. The team will use a special robotic tool to film the area and get samples of the exposed mantle. They hope to study everything from the chemistry of the oceans to how the Earth's surface behaves under the sea.
What's the title for the passage?

A．How to study the earth.

B．The formation of the earth.

C．A hole in the earth.

D．Studying the inside of the earth.

For the main layers of the earth, which one is right?

A．crust, mantle, core	B．seabed, crust, mantle
C．seabed, mantle, core	D．crust, seabed, core

How does the hole come into being?

A．It's because of a volcano eruption.

B．It's because of the plates movements

C．It's because lava rushes up from the mantle

D．It's not clear from the passage.

By studying the hole, the scientists want to do the following except____.

A．knowing what's below the Earth's surface

B．getting samples of the exposed mantle

C．getting the film of the hole

D．studying the chemistry of the oceans