23. not all = all not 并不都 not every = every...not 并非每个...都 not both=both not 并非两个都...
Not all of them were safe.=All of them were
not safe.
Not both of the students are good at
English. =Both of the students are not good at English.
完全否定：None of
the rooms are safe. / Neither of the students is good at English.