Which of the following statements is not true?
a. you are exposed to nuclear radiation everyday.
b. most of the nuclear radiation you are exposed to occurs naturally in the environment.
c. naturally occurring nuclear radiation is called background radiation.
d. all natural radiation is at a level low enough to be safe.

Option D

Explanation:

There are three major sources of background natural resources a) Terrestrial Radiation

; b) Internal Radiation and c) Cosmic Radiation

Cosmic Radiation is the radiation received from sun and stars. These radiations are received in traces as they go through different filters such as earth’s atmosphere, its elevation and magnetic field.  

Terrestrial Radiations are received from radioactive minerals like uranium, radium and thorium. Since these minerals exists in soil and rock, their exposure is not harmful to mankind

Internal Radiation exists within the body of humans as radioactive potassium-40 and carbon-14 is presents with in the body since birth

Hence, option D is correct

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.