The scientists do a tiger_____once year to know their number.(count)

The scientists do a tiger_____once year to know their number.(count)
The scientists do a tiger_____once year to know their number.(count)

The scientists do a tiger_____once year to know their number.(count)

The scientists do a tiger counting once per year in order to know their number.

空中应填counting
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把count变成counting填进去就可以了。另外应该是once a year 每年一次。

用“count” , 因为“do a count ” 是“清点”的意思，所以这里的“do a tiger count ”是清点老虎数量的意思。整句话的意思就是“科学家每年清点老虎一次，以便知道它们的数目”。 另外 "once a year" "每年一次"。