Researchers have tinkered with some antiviral treatments that might work against a wide spectrum of diseases, but all have had shortcomings. Now one group thinks they have found a method that might protect cells in the body from a viral invasion.
In the second sentence, the part - "Now one group thinks they have found" - should not it be one group thinks
it has found ?
Can some one please clarify what is the rule working here ?
Many thanks in advance !
Regards,
Andy