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heard of since heard since heard before heard of before
were released had been released would have been released was releaseD.
proves that the epidemic has been spreading very fast over the past eight years implies that the USAID was not very successful in the past eight years shows that the epidemic has spread too fast to be controlled over the past eight years explains that the epidemic has been controlled
were have made have been have become
when how far how soon how long
in; for on; in on; for in; since
open be open been open been opened
died dead were dying have been dead
has been was had been will be
were have made have been have become
when during which since when since then
in; for on; in on; for in; since
How often How soon How far How long
were became have been have made