People living at sea level have around $5$ million $RBC$ per cubic millimeter of their blood whereas those living at an altitude to $5400$ metres have around $8$ million. This is because at high altitude

  • [AIPMT 2006]
  • A

    people eat more nutritive food, therefore more $RBCs$ are formed

  • B

    people get pollution­free air to breath and more oxygen is available

  • C

    atmospheric $O_2$ level is less and hence more $RBCs$ are needed to absorb the required amount of $O_2$ to survive

  • D

    there is more $UV$ radiation which enhances $RBC$ production.

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The soil organisms are

$A$... regulators are able to maintain homeostasis by means which ensures constant body temperature, constant osmotic concentration, etc. All ...$B$... and ...$C$.... and is very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation)

Evolutionary biologists believe that the 'success' of mammals is largely due to their ability to maintain a constant body ...$D$... and thrive whether they live in Antarctica or in the Sahara desert
Choose the correct option for $A , B , C$ and $D$

$A$ - The salt concentration is less than $5$ (parts per thousand) in inland waters.

$R$ - The salt concentration is $45 -50$ (parts per thousand) in the sea.

Which element is responsible for causing soil salinity ? At what concentration does the soil become saline ?

Find out correct match w.r.t. salinity (in parts per thousand)