All the people in the stadium cheered up when they saw hundreds of colorful balloons __________ slowly into the sky.

单项选择题We shall probably never be able to __________ the exact nature of these sub-atomic particles.

单项选择题The financial problem of this company is further __________ by the rise in interest rates.

单项选择题The medicine __________ his pain but did not cure his illness.

单项选择题It was __________ that the restaurant discriminated against black customers.

单项选择题Professor Hawking is __________ as one of the world's greatest living physicists.