He was so deep in thought, thinking of the problem ________he knocked into the tree without noticing it.
18. It was because of English girlfriend, believe it or not, ______ his English improved so greatly.
It was lack of money, not of effort, _____ defeated their plan.
I don’t know _____makes her afraid of having her business discussed.
15. It was with great joy _____ he received the news ______ his lost daughter had been found.
It was _____back home after the experiments.