When lava reaches the surface of the Earth through volcanoes or through great fissures the rocks that are formed from the lava cooling and hardening are called extrusive igneous rocks. Some of the more common types of extrusive igneous rocks are lava rocks, cinders, pumice, obsidian , and volcanic ash and dust.
Signal detection theory is a theory that predicts how and when one detects the presence of weak stimuli admits background noise. The detection of stimuli involves decision and sensory processes. Factors that influence this detection include the intensity of the stimuli, physical factors such as fatigue and healthiness, and psychological factors such as motivation and expectations.
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1) c. 2 m/s
Explanation:
The relationship between frequency, wavelength and speed of a wave is

where
v is the speed
is the wavelength
f is the frequency
For the wave in this problem,
f = 4 Hz

So, the speed is

2) a. 2.8 m/s
The speed of the wave on a string is given

where
T is the tension in the string
is the linear mass density
In this problem, we have:
(final tension in the rope, which is twice the initial tension)
--> mass density of the rope
Substituting into the formula, we find

Answer:
The correct option is;
D. Folding of Rock
Explanation:
A fold in structural geology, is wave like form of stratified rock arrangement due to the bending of rocks which where originally deposited as flat rocks but became warped in the course of deformation of the rock layers.
The degree of bending can be very gentle such that the zig zag orientation of the rock is hardly noticeable. The bending can also very evident and in some cases the two layers may be bent up to 180, making the individually different strata once again parallel to each other.