Answer is $\text{D}.$ Both India and UK
Here's How :
Total number of visitors from India are $3$ and $4$ are from UK.
India on Day $1$ has $1$ visitor which could be from University $1,2,5,6$ and $7$. On the second day India has two visitors, one could be from University $3$ and other from University $8.$ So three distinct universities can be covered.
UK has $2$ visitors on Day $1$ which could be from Universities $1,2,5,6$ and $7$ and $2$ visitors on Day $3$ who could be from University $4$ and $6.$ Even if Visitor from University $6$ is common, the other three must be distinct because University $6$ makes only one visit on Day $1.$
Other countries cannot host three distinct Universities because they have less than $3$ visitors.