_____ many times, he finally understood it.
_________ he met with the difficulty did he realize the importance of our help.
Eating too much fat can __________ to heart disease and high blood pressure.
Due to the unreasonable individual income __________,the gap between the rich and poor has become an outstanding issue.
He contributed an article __________ China Daily.
Thomas Alva Edison was __________ American inventor and __________ businessman who developed many devices, such as __________ bulb, that greatly influence life worldwide.