pleasant, pleasing, pleased
(1) pleasant 可作定语和表语。修饰事物，不能修饰人。因此句子的主语只能是表示事物的词语，而不能是人。意思是“令人愉快的，令人高兴的”。
I hope you'll have a pleasant holiday.
我希望你能过一个愉快的.假期。
(2) pleasing “令人高兴的，令人愉快的”，表示宁静、满意、令人满足之意。侧重于表示接受对象的情感，传递主观感受。比 pleasant 稍弱。主语可为人或事物。
An actor should have a pleasing personality.
表演者应当具有一种令人愉快的个性。
(3) pleased “高兴的，感到满意的”含义与glad基本相同。作表语时，句子的主语只能是“人”，而不能是表示事物的词语。be pleased with 表示“对……表示满 意”之意。
She had a pleased look on his face.
她脸上露出了满意的表情。
burn down, burn up, burn out
bum down 指“烧为平地，烧毁”;也指“火力减弱”。
The house was burnt down in an hour.
房子一小时被烧为平地。
bum up 有“烧旺”之意，也可指“消耗掉”。
You'd better put more wood on the fire to make it burn up.
你往火上添着柴，让它烧旺。
bum out 指“火熄灭”。
The fire had burnt out before I returned.
在我回来前，火已经熄灭了。
elect, select, choose
elect 只能用于选举人，是投票选举的正式用语。
They elected Nixon President. 他们选尼克松为总统。
choose 可用于挑选人或物。
It's hard for me to choose one from so many pairs of shoes.
要从这么多双鞋子当中挑选一双对我来说真是太难了。
select 意为精心挑选，多用于物。
She selected a pair of socks to match her suit.
他精心挑选了一双袜子来与衣服搭配。
be known for, be known as, be known to
be known for 以……出了名 (通常不是指同位的关系)
be known as 作为……出了名 (通常加上职业名词，表同位关系)
be known to为……所知
Japan is known for its cars.
日本以它的汽车而闻名。
Luxun is known as a writer.
鲁迅作为作家很出名。
As is known to all, China has four famous invitations.
众所周知，中国有四大的发明。
observe, watch
当“观察”来讲时，observe相当于watch carefully，尤其用于实验或研究等场合。具体来说，observe含有“察觉到”的意思，watch意为“盯着看”。
watch还含有“观看(比赛、电视)”等，而observe没有此意。另外，watch还有“照料”之意，相当于take care of。还有“当心”之意，相当于be careful with。
She has observed the stars all her life.
她一生都在观察星星。
I'll watch the baby while you are away.
你不在时，由我照料你女儿。
You'd better watch Mr Smith, I think he is
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