Question

Which of the following sentences uses a signal phrase to introduce content from an outside source?

Schools like Harvard conduct studies about butterflies every year.
"The migration of the monarch butterfly is a sight to celebrate" (Professor X).
According to a study by Harvard University, the migration of the monarch butterfly is a sight to celebrate.
Monarch butterflies go through a migration process each year, according to recent studies.

Answer 1

According to a study by Harvard University, the migration of the monarch butterfly is a sight to celebrate.