Read the text and choose the correct options to answer the questions
There are hundreds of natural phenomena which fascinate or threaten people all over the world. Some of them are dangerous, others are not. Let's get a closer look at one of the most unusual and rare among them.

Frozen methane bubbles. When the ice is crystal clear, you can see the bubbles looking like plates or coins stuck in the frozen water of some lakes. These circles are, in fact, the result of methane gas that is produced by microorganisms. When dead organic matter, like leaves, insects or animals, falls into the water, it becomes a nutritious food source for organisms living in the lake. The latter eat this dead matter and excrete methane. Then the byproducts of bacteria digestion are released and they bubble up from the bottom of the lake and get trapped in the ice. If you poke a small hole in such a disc, you will get the stream of the greenhouse gas coming out. It's very dangerous to light matches near these holes because methane is highly flammable. Therefore, this marvellous phenomenon makes an amazing, but dangerous sight.

Enormous amounts of methane are trapped in Lake Baikal in Russia, Lake Abraham in Canada and some other big bodies of water. If being released, this gas will make serious implication to the planet-heating and will contribute to global warming.

What are the frozen methane bubbles?

• a natural phenomenon.
• a man-made phenomenon.

What is dead organic matter?

• Organic litter thrown into the water.
• Plants and animals sunk in the water.

What produces methane?

• Dead organic matter.
• Bacteria.

How can you check whether the bubble contains methane or not?

• Make a small opening in it.
• Check the colour of the bubble.

Is it funny and safe to poke the methane bubbles?

• Yes, they explode making a loud sound.
• No, it's hazardous.

Why is methane extremely dangerous?

• Because it's an asphyxiant gas.
• Because of its ability to burn and explode.

Is methane one of the most potent greenhouse gasses?

• Yes, it has a big impact on the greenhouse effect.
• No, it has no influence on the environment.