Is not only the most valuable precious metal, but it is also both aesthetically and intrinsically pleasing, and retains religious or symbolic meaning in many cultures.
a. silver
c. iron
b. bronze
d. gold

The correct answer is option d, that is, Gold.  

Explanation: Gold can hold various distinct significances, in terms of economy, it can attain material value, in social contexts it can acquire meaning for position and status within an ordered composition, and in terms of religion, it can be used to articulate admiration of the divinity or a divine.  

The symbolic nature of gold can be illustrated as a means of communication, this signifies, firstly, communication between the humans in distinct conditions for distinct purposes, however, also secondly between the humans and a spiritual world.  

d

Explanation:

14 days is the half-life of phosphorus-32