1. If we can make ________most of renewable energy sources, there will be _______big rise in the environmental quality.
A. /, / B. the, a C. the, / D. /, a
2. Native English speakers can understand each other ________they don’t speak the same kind of English.
A. only if B. so long as C. in case D. even if
3. It was not until the subprime loan crisis（次贷危机） _______ great damage to the American financial system that Americans _______ the severity of the situation.
A. caused, realized B. had caused, realized
C. caused, had realized D. was causing, had realized
