________ how others react to the book you have just read creates an added pleasure.

(2012·辽宁高考)This machine is very easy ________. Anybody can learn to use it in a few minutes.

Do you consider it any good _____ psychology?

_____such heavy pollution already, it may now be too late to clean up the river. 

________ global energy safety, all the countries have been called on to take joint efforts ．