Select the most appropriate option to fill in the blank.

I inherit all that humanity __________ during tens of thousands of years and to all that it has thought, felt and suffered.

has achieved

The most appropriate option to fill in the blank is have achieved.

The sentence is about the speaker inheriting all that humanity has achieved during tens of thousands of years. The speaker is not talking about something that is happening now, but something that has already happened. Therefore, the past tense "have achieved" is the most appropriate option.

The other options are not as appropriate.

• Has achieved is the present perfect tense, which is used to talk about something that happened in the past but has a connection to the present. In this case, there is no connection between the past achievements of humanity and the present, so the present perfect tense is not the right choice.
• Were achieving is the past progressive tense, which is used to talk about something that was happening in the past but is no longer happening. In this case, the achievements of humanity are still happening, so the past progressive tense is not the right choice.
• Are achieving is the present tense, which is used to talk about something that is happening now. In this case, the achievements of humanity are not happening now, but have already happened, so the present tense is not the right choice.