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US navy Captain Mark Matthews is not prepared to say whether his crew located the "black box" from Malaysia Airlines Flight MH370.

"I don't want to build up anyone's hopes," said Matthews, the navy's supervisor of salvage and diving.

"We are working within a 3-mile (4.8-km) grid and it is painstakingly slow work."

The search area in which the Australian Defence Force vessel Ocean Shield is operating is about 1,800 km west of Perth, the capital of Western Australia state.

Ocean Shield, which detected the pings late on Saturday night and on Sunday morning, is towing a pinger locator at speeds of 3.7 to 9.3 km per hour, Matthews said.

The towed underwater vehicle can detect signals from locator beacons attached to the black box.

"What it has detected so far are pulses consistent with the flight data and cockpit voice recorders," Matthews said.

But the battery life of the beacon was fast running out on Monday, 31 days after the Boeing777 with 239 passengers and crew disappeared.

All those involved in the search say the battery life can run for 40 to 45 days. But the pulses will become gradually weaker.

"I would be more confident if we could relocate those signals again," Matthews said.

"The pinger locator can track to depths of 3,000 to 6,000 meters. The problem we face is that the Bluefin-21 autonomous underwater vehicle we have can only operate to a maximum depth of 4,500 meters.

"We think the wreck site is at that depth but really don't know. Water around there varies from 5,000 to 6,000 meters. It is very, very deep.

"Am I confident we have found the site of the aircraft? I can't say. I will need to wait until I can get an assessment from my crew."

Questions:

1. Who is the US Navy’s supervisor of salvage and diving?

2. What is Ocean Shield?

3. At what speed is the pinger locator towed behind the vessel?

Answers:

1. Capt. Mark Matthews.

2. An Australian Defence Force vessel.

3. At speeds of 3.7 to 9.3 km per hour.

（中國日報網(wǎng)英語點津 Helen 編輯）

About the broadcaster:

Anne Ruisi is an editor at China Daily online with more than 30 years of experience as a newspaper editor and reporter. She has worked at newspapers in the U.S., including The Birmingham News in Alabama and City Newspaper of Rochester, N.Y.