Explanation

The reason is that the rails expand in summer

. The gap is provided to allow for this expansion.

If no gap is left the expansion in summer will cause the rails to bend sideways

This may result in train accidents.

Explanation

 "Meter per second" (m/s) is the standard unit of speed and velocity,

Indicating the distance traveled in meters throughout one second.

It measures how fast something moves (speed) and in what direction (velocity). 

Speed:

Speed is a scalar quantity, meaning it only describes the magnitude (how fast) of an object's movement, measured in meters per second. 

Velocity:

Velocity is a vector quantity, meaning it describes both the magnitude (how fast) and direction of an object's movement, also measured in meters per second. 

Explanation

 The science of treating the muscular and skeletal system, also known as the musculoskeletal system, is called orthopedics. 

Explanation

 The pulse rate is a measurement of the heart rate, or the number of times the heart beats per minute. 

Explanation

 The main purpose of white blood cells, also known as leukocytes, 

  They protect the body from infection and disease by fighting off harmful pathogens and other foreign substances. 

Explanation

 Blood comprises approximately 60% plasma and 40% blood cells (corpuscles),

Including red blood cells, white blood cells, and platelets. 

Explanation

During sleep, a man's blood pressure typically decreases or "dips" compared to daytime levels, following the natural circadian rhythm. 

Explanation

Pertussis is commonly known as whooping cough. 

Explanation

 Out of the options provided, influenza is not a waterborne disease, while cholera, amoebiasis, and typhoid are. 

Explanation

Hypothalamus is responsible for temperature regulation.

It helps maintain the body's internal temperature by triggering responses like sweating or shivering.