Choose the correct form of the words in brackets to complete the following sentence.
By the time Yang Liwei (become) became || had become || was become the first person sent into space by the Chinese Space Program in 2003, NASA (send) had sent || sent || has sent over 100 people.
Solutions:By the time Yang Liwei became the first person sent into space by the Chinese Space Program in 2003, NASA had sent over 100 people.
