[TABLE="width: 80"]
<tbody>[TR]
[TD="align: center"][/TD]
[TD="align: center"]A[/TD]
[TD="align: center"]B[/TD]
[/TR]
[TR]
[TD="align: center"]1[/TD]
[TD="align: center"] JOHN [/TD]
[TD="align: center"]MICHAEL[/TD]
[/TR]
[TR]
[TD="align: center"]2[/TD]
[TD] TASKA[/TD]
[TD="align: center"]TASK D[/TD]
[/TR]
[TR]
[TD="align: center"]3[/TD]
[TD] TASKB[/TD]
[TD="align: center"]TASK E[/TD]
[/TR]
[TR]
[TD="align: center"]4[/TD]
[TD]TASKC[/TD]
[TD="align: center"]TASK F[/TD]
[/TR]
</tbody>[/TABLE]
1. First make a table like this.
2. Now select "TASK A" to "TASK C". Right click, name cells as "JOHN". Then select "TASK A" to "TASK C". Right click, name cells as "MICHAEL".
3. Select cell C1. Go to "Data" tab. Click "Data Validation". In the little window there is a dropdown. Select "List". List source "$A$1:$B$1".
4. Select cell C2. Go to "Data" tab. Click "Data Validation". In the little window there is a dropdown. Select "List". List source "=INDIRECT($C$1)".
This should give you an idea. You can modify all these according to your scenario. Have a nice day!