First, we had lunch and then our guide told us the secret of the cave, whichpleased me. 
句子中有一系列的动作、感受，我们不知道到底什么原因使作者感到 pleased。是the cave’s secret吗？是因为guide 抖出秘密？是 lunch？是因为秘密在吃过午饭后才被抖出（had lunch and then our guidetold us…）？Which 到底所指为何？
I was pleased that the guide waited until after lunch to tell us the secret.
I was pleased with the secret of the cave, which the guide told us after lunch.
From the mid-1960s, especially during the Vietnam War, American youngstersstart an anti-Vietnam War and anti-establishment campaign (the so-called hippieculture, which was just a passive resistance without positive creativity).
During the mid-1960s, in the midst of the Vietnam War, American youth launchedanti-war and anti-establishment campaigns (the so-called hippie culture wasmerely passive resistance without constructive contribution).
At that time, many people began to pay attention to some problems ofenvironment, sanitation and ecology, which put pressure on the government tolegislate for the preservation of environment and against pollution.
When people became aware of the environmental, health and ecological problems,the government was pressured into enacting legislation to address the problems.
Prosperity of economy raises the standard of living, which is associated withthe higher requirement from people who hope to live better and better, whocannot stand living standards going from bad to worse, or even no change nochange of living standard.
As part of human nature, when the standard of living rises with economicdevelopment, expectations go up. Expectations will never come down. Evenremaining at status quo is unacceptable.
Obviously, this is an “ideal realm”, which we may not reach in a decade or even in acentury.
Obviously, this is an ideal situation (which is) impossible to achieve within adecade or even a century.
注：括号中的 which is 可略。见下文说明。
“who is”、“which was”通常多余，可以删除：
His brother, who is a member of the same firm
His brother, a member of the same firm
Trafalgar, which was Nelson's last battle
Trafalgar, Nelson's last battle
He washed all the flasks, and then he locked up the lab.
and 表示句子增加了信息。But 则意味着行为的逻辑顺序有所调整。什么时候用and，什么时候用but，取决与作者意图。
(1) He washed all the flasks, then he locked up the lab.
(2) After he washed all the flasks, he locked up the lab.
He washed all the flasks before he locked up the lab.
(1) 强调各环节顺序（先洗水壶，然后把实验室锁上）；(2) 则强调洗水壶的行为（washing up the flask）
The most important solution is changing the education pattern which will notlead a hi-tech student to a robot and will make a philosophy student know thenature of science.
The focus should be to change our education, so that 【体现因果关系】science learners do not become “machines” and humanitieslearners will have some knowledge of science.