In the past, some cities experienced "killer fogs," dense, smoky fogs that actually resulted in the deaths of some people. Find out more about these killer fogs, including which cities were affected by them, what caused them, and why they no longer occur.

Explanation below

Explanation:

The air is one of the things that can become harmful to people when polluted. The air is considered to be polluted when there is a release of harmful gases through the burning of fuel such as coal, petrol, kerosene, wood and soon. This is usually known as air pollution.

The burning of fuel, which is known as combustion usually cause the release of heavy smoke into the atmosphere. This smoke is usually filled with harmful gases such as methane and Carson oxide.

The most popular example of killer fog event occurred in London in the year 1952. At this time, most of the companies make use of coal as fuel. This event caused the death of about 6000 people in about two weeks. But the event is not likely to occur again now, because the use of coal by companies has been stopped and LPG has been used as the replacement.

Another one is the effects from the 1948 killer smog in the steel town of Donora, Pennsylvania, which left at least 20 dead and dozens more injured.

While Tehran also experienced a killer fog after 60 years of that of London's effect.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.