External depreciation may be defined as a loss in value caused by an undesirable or hazardous influence offsite. 
<h3>What is depreciation?</h3>
Depreciation may be defined as a situation when the financial value of an acquisition declines over time due to exploitation, fray, and incision, or obsolescence. 
External depreciation may also be referred to as "economic obsolescence". It causes a negative influence on the financial value gradually. 
Therefore, it is well described above. 
To learn more about Depreciation, refer to the link:
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C my friend 20 characters suck
        
             
        
        
        
Answer: 
B A and C
Explanation:
Given:
Specimen         σ σ
                      σ
A                       +450                      -150
B                       +300                      -300
C                       +500                      -200
Solution:
Compute the mean stress
σ =  (σ
 =  (σ +  σ
  +  σ )/2
)/2
σ =  (450 + (-150)) / 2
 =  (450 + (-150)) / 2
        =  (450 - 150) / 2  
        = 300/2
σ = 150 MPa
 = 150 MPa
 
σ = (300 + (-300))/2
  = (300 + (-300))/2
         = (300 - 300) / 2
         = 0/2  
σ = 0 MPa
  = 0 MPa
   
σ = (500 + (-200))/2
  = (500 + (-200))/2
         = (500 - 200) / 2
         = 300/2
σ = 150 MPa
  = 150 MPa  
Compute stress amplitude: 
σ =  (σ
 =  (σ -  σ
  -  σ )/2
)/2     
σ =  (450 - (-150)) / 2
 =  (450 - (-150)) / 2
        =  (450 + 150) / 2 
        = 600/2
σ = 300 MPa
 = 300 MPa
σ =  (300- (-300)) / 2
 =  (300- (-300)) / 2
        =  (300 + 300) / 2
        = 600/2
σ = 300 MPa
  = 300 MPa
σ = (500 - (-200))/2
  = (500 - (-200))/2
         = (500 + 200) / 2
         = 700 / 2
σ = 350 MPa
   = 350 MPa 
From the above results it is concluded that the longest  fatigue lifetime is of specimen B because it has the minimum mean stress.
Next, the specimen A has the fatigue lifetime which is shorter than B but longer than specimen C.
In the last comes specimen C which has the shortest fatigue lifetime because it has the higher mean stress and highest stress amplitude. 
 
        
             
        
        
        
In an alternating current (AC) circuit the two poles alternate between negative and positive and the direction of the current (electron flow) reverses periodically.