请问：a.m.和p.m.结尾时要加句号吗？谢谢！

a.m.、p.m.、etc.是缩写词，有关标点符号的用法如下：
出现在句尾时，如果句尾是句点（句号），则句点（句号）可省略，但a.m.、p.m.、etc.本身后面的点需保留，如（1）。如果句尾是问号，则不可省略a.m.、p.m.、etc.后面的点以及问号。
出现在句中，或者后面接逗号、破折号、冒号时，a.m.、p.m.、etc.的点不可省略，如（2）（3）（4）。
（1）yorktown
daily
is
slowing
updates
as
the
storm
moves
through
virginia,
effectively
stopping
regular
updates
at
10
p.m.
（2）
we
will
be
back
reporting
at
7
a.m.
tomorrow.
（3）
voting
sites
across
the
county
will
be
open
from
7
a.m.
to
7
p.m.
tuesday
in
the
republican
and
democratic
party
primaries.
（4）the
access
ramps
from
telegraph
road
southbound
and
northbound
to
the
inner
loop
(i-95/495
south)
will
be
closed
during
daytime
hours
for
roadway
construction
from
monday,
may
9
through
thursday,
may
12
from
9:30
a.m.
–
3:30
p.m.,
and
on
friday,
may
13
from
9:30
a.m.
–
noon.
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