The correct answer is: No zoologist has been able to keep a gorilla under close observation in the dark jungles in which he lives.
The reason is that the present perfect tense is used to talk about actions that started in the past and continue to the present. In this case, the action of keeping a gorilla under close observation in the dark jungles is something that zoologists have been trying to do for a long time, but they have not been successful.
The other options are incorrect because they use different tenses. The past tense is used to talk about actions that happened in the past and are not happening anymore. The future tense is used to talk about actions that will happen in the future. The past perfect tense is used to talk about actions that happened before another action in the past. The present perfect progressive tense is used to talk about actions that started in the past and continue to the present, but with an emphasis on the ongoing nature of the action.
In this case, the past tense, future tense, past perfect tense, and present perfect progressive tense are all incorrect because they do not accurately describe the action of keeping a gorilla under close observation in the dark jungles. The present perfect tense is the only tense that accurately describes this action.