Questions

The olfactory system is the only system in which the receptors send their signal directly to the higher brain and bypass the thalamus, which normally acts as a filter for the processes of the lower brain.

The Great wall is a mighty monument to the building skill of ancient China. This wall, built of stone and earth to a height of 6 metres and extending over 2400 kilometres of hills and valleys, links the east coast with the mountains of the west right across northern China. The wall was wide enough for a carriage to go through.At intervals of every few hundred metres were located watch towers for warriors. Such a large study construction must have taken decades and an army of labourers to complete it. 

We know that, preceeded means to come before. 

Hence, the given sentence, preceded in death means that person had died before this person.

For example :: Rahul preceeded Ravi in death, means Rahul died before Ravi.

First Generation  Vacuum Tubes (1940-1956)

The first computer systems used vacuum tubes for circuitry and magnetic drums for memory

A solution is a homogeneous type of mixture of two or more substances.

A solution has two parts::

1. A solute and

2. A solvent.

The solute is the substance that dissolves, and the solvent is the majority of the solution.

Caspian Sea (371,000 sq km)

In chemistry, a metal is an element that readily forms positive ions (cations) and has metallic bonds. Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances.

Examples of metals are aluminium, copper, iron, tin, gold, lead, silver, titanium, uranium, and zinc.

Here Se - Selenium is an element but is not a metal, S - Sulphur is not a metal and I - Iodine is also not a metal.

Hence, Zn - Zinc is the only metal in the given options.