user: What was the cause of MH370 flight's disappearance?

assistant: There are many conspiracy theories surrounding the disposition of the flight, ranging from a military downing, aircraft hijacking, terrorist attack, to a pilot suicide over his deteriorating personal life, but all of these suggestions have not been proven substantially.  We will really never know, and will just have to leave this an unsolved mystery.

user: Where is Silicon Valley geographically based?

assistant: Silicon Valley is in the San Francisco Bay Area of California

user: What are the tennis ball made of?

assistant: Nowadays most tennis balls are made of hollow vulcanized rubber with a felt coating.