Replace All the Batteries
There is a device using four units of batteries.
One day it failed to operate. But I experienced the same situation several times before.
So, I exchanged two batteries which looked older, as before. Whenever I replaced two older batteries among the four, it was restored. But this time it didn't work.
So, I checked it by disassembling it and using some method to find that a switching unit connected to the main body over a wire properly worked.
Accordingly I went out to buy a new main body. But when I checked it at home I found something strange. The new main body with two new batteries and two existent batteries (those relatively new among the four old batteries) did not work, either. So, I replaced the two existent batteries with two other new ones. It worked.
I should have replaced all the four batteries at once.
So, finally I got one new lesson and one new device redundant at hand.
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Mar 11:27 And they come again to Jerusalem: and as he was walking in the temple, there come to him the chief priests, and the scribes, and the elders,
Mar 11:28 And say unto him, By what authority doest thou these things? and who gave thee this authority to do these things?
Mar 11:29 And Jesus answered and said unto them, I will also ask of you one question, and answer me, and I will tell you by what authority I do these things.
Mar 11:30 The baptism of John, was it from heaven, or of men? answer me.