B4

During winter and sometimes even autumn and spring it snows in some cities of southern Brazil. There are several cities known for their snow, like Urupema and Urubici.
(Participle II, “известные”, подходит по смысловому контексту)

 KNOW

B5

These cities are all in high areas, but even places at sea level can have snow, although in small amounts and not every year.
(they - are)

 BE

B6

Brazil is thought to be a “tropical paradise” which is very wrong. Foreigners who travel to southern Brazil during autumn or winter in search for some heat and beaches are often disappointed.
(present simple passive, т.к. это общее утверждение. О Бразилии думают, а не Бразилия думает)

THINK

B7

Do you know how the global warming affects the Arctic? A survey by the Japan Agency for Science and Technology shows that Arctic ice is melting at a far quicker rate than anticipated. Today Arctic ice is melting at previously unseen rates.
(степень сравнения)

 QUICK

B8

The coastal ice in parts of Canada and Alaska has become quite brittle. Ice easily breaks away in large pieces and melts in the open ocean. Now there is also less sea ice in the Arctic Ocean.
(степень сравнения)

 LITTLE

B9

It happens because ice floats/has floated into the Atlantic Ocean.
(present simple, лёд плывет в Атлантический океан – общее утверждение. 
present  perfect, автор хочет показать, что лёд плывет в Атлантический океан, и уже есть результат)

FLOAT

B10

Scientists say that the lack of ice represents clear proof that the planet is warming. Back in the past it could take three years to get through the waterway's thick ice successfully, now - just a few weeks.
(present continuous, т.к. это изменение, развитие. Планета постепенно нагревается)

WARM