D it is
A. has emerged from an animal host in less populated regions of Africa where there is more frequent contact[present perfect tense is not required] wrong
B. was emerging from an animal host in a sparsely populated region of Africa where there is contact more frequent[past continuous tense is wrong, the construction of B is also wrong where there is contact more frequent is wrong]
C. emerged from an animal host where there is more frequent contact in a sparsely populated region of Africa["where"must modify a place, here it is modifying animal host, less populated regions is better] wrong
D. emerged from an animal host in less populated regions of Africa where there is more frequent contact [perfect and right] parsely populated
...
A. has emerged from an animal host in less populated regions of Africa where there is more frequent contact[present perfect tense is not required] wrong
B. was emerging from an animal host in a sparsely populated region of Africa where there is contact more frequent[past continuous tense is wrong, the construction of B is also wrong where there is contact more frequent is wrong]
C. emerged from an animal host where there is more frequent contact in a sparsely populated region of Africa["where"must modify a place, here it is modifying animal host, less populated regions is better] wrong
D. emerged from an animal host in less populated regions of Africa where there is more frequent contact [perfect and right] parsely populated
...
