Stress Package not working

Hello Everybody,
I'm trying to execute Lab 2.6, but I get an error when starting the service. Is there anyone who found the same problem that can help me?
This is the error I get

● foo.service - Example service unit to run stress
Loaded: loaded (/lib/systemd/system/foo.service; disabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Mon 2020-09-21 07:35:01 UTC; 6s ago
Process: 1223 ExecStart=/usr/bin/stress --cpu (code=exited, status=1/FAILURE)
Main PID: 1223 (code=exited, status=1/FAILURE)

Sep 21 07:35:01 learningplatform systemd[1]: Started Example service unit to run stress.
Sep 21 07:35:01 learningplatform stress[1223]: stress: FAIL: [1223] (160) missing argument to option '--cpu'
Sep 21 07:35:01 learningplatform systemd[1]: foo.service: Main process exited, code=exited, status=1/FAILURE
Sep 21 07:35:01 learningplatform systemd[1]: foo.service: Failed with result 'exit-code'.
root@learningplatform:/home/francesco# systemctl status foo -l

Thank you in advance.