Q: This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
Passage: In October 2006, the Bill & Melinda Gates Foundation was split into two entities: the Bill & Melinda Gates Foundation Trust, which manages the endowment assets and the Bill & Melinda Gates Foundation, which "... conducts all operations and grantmaking work, and it is the entity from which all grants are made". Also announced was the decision to "... spend all of [the Trust's] resources within 20 years after Bill's and Melinda's deaths". This would close the Bill & Melinda Gates Foundation Trust and effectively end the Bill & Melinda Gates Foundation. In the same announcement it was reiterated that Warren Buffett "... has stipulated that the proceeds from the Berkshire Hathaway shares he still owns at death are to be used for philanthropic purposes within 10 years after his estate has been settled".
A:
When must shares be spent for the foundation?