According to scientists, our mental abilities begin to _______ from the age of 27 after reaching the highest level at 22．

The accident has _____________to be a good thing after all．

There’s no way of knowing why one man makes an important discovery ___ another man, also intelligent, fails.

The rainiest said, “We are ready for discussion with any legal parties, but we’ll never    with enemies.”

After the new technique was introduced，the factory produced ________ cars in 2011 as the year before.