What's the difference between decrease,descend,decline and lessen. And how can I use it properly?? Better with some examples

Thanks!!!

compare the following two sentences which one is better?? There,the productivity declines,while price and unemployment rate soar.

There,the productivity has declined ,while price and unemployment rate have soared.

Translation homework Please help me correct it and make it more fluent Thanks!!! Ensuring food for all is the most basic right of for human survival and also it is the foundation among all the human right. Great progress has been gained in agricultural domain around the globe,but hunger and poverty remain a silent crisis troubling all the mankind. More than 800 million people in the world still live under the threaten of food shortage and malnutrition.   

It remains a major challenge and a shared responsibility for all mankind to boost the agriculture and eliminate hunger and poverty. The international community should work together to strengthen the agriculture collaboration. More attention should be attached on developing countries,especially for some least developed countries. Trade protection should be lessened;the support of agriculture technology and funds for the least developed countries should be enhanced and the global agriculture productivity and food security should be improved.

Admire or appreciate ??? How to use these two words properly?? What's the difference?? Thanks a lot !!

How to express my thanks to my close friends without using thanks/thank you/cheers. I don't wanna be too formal so what would a native speaker say in daily life

Thanks

exultant triumphant Any difference?? Thanks!

vital,critical,essential,important What are the differences???