Answer:
The correct option is A. A directory of relatives' phone numbers
Explanation:
Family communication plan is a measure taken to contact the relatives of a person if an emergency situation arises for a person. In today's modern world, emergencies can happen at any time so it is very important to have a family communication plan so that the relatives of a person be informed immediately. Hence, option A is correct.
Other options are false because none of the other options will be usable in case of an emergency.
C. because there is a property of acids which stat that they turn litmus papers red instead of blue.
D - an increase in tree cover in the tundra.

Absolute Dating
AKA. RADIOMETRIC DATING
We can learn about the past by studying the present.
The Principle of Uniformitarianism states that current geological processes are the same processes that were at work in the past. This principle was proposed by Charles Lyell in the 1800's
Absolute Dating
Involves finding the absolute age (actual age) of a rock or fossil.
Elements that emit particles and energy are radioactive.
As radioactive elements emit particles and energy, they form new isotopes or elements.