Answer:
Following system of equations have exactly one solution:

Step-by-step explanation:
Given 4 system of equations:
1st

2nd

3rd

4th

To find: Which system of equations has only one solution?
Solution:
First of all, let us learn the concept.
Let the equation of lines be:
and 
1. No solution:
There exists no solution if:

2. Infinite solutions:
There exist infinitely many solutions if:

3. One solution:
There exists one solution if:

Now, let us consider the given equations one by one.
1st system of equations:
The ratio is:

So, no solution.
2nd system of equations:
The ratio:

So, infinitely many solutions.
3rd system of equations:

So, no solution.
4th system of equations:

Hence, <em>only one solution.</em>
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<em>So, the answer is:</em>
Following system of equations have only one solution:
