Each advisor was contacted by his students.

my reply
2. Each advisor was contacted by his or her students.

Right. Of you could change it to All advisors were contacted by their students.

To change the sentence "Each advisor was contacted by his or her students" to "All advisors were contacted by their students," you can follow these steps:

1. Replace the phrase "each advisor" with "all advisors" to indicate that multiple advisors were contacted.
2. Replace the pronoun "his or her" with the pronoun "their" to be gender-neutral and represent the plural noun "advisors."

By making these changes, the revised sentence will accurately convey the idea that all advisors were contacted by their students.