options: -n
	
	make -n 
	make --just-print
	#donot exec cmd while just print cmd in oeder.
options: -s
	make -s 
	make --silient
	make --quiet
	#forbit completely exec cmd. it will make option '-w' disable.

options: -k
	make -k 
	make --keep-going
	#even though an error occurs while executing a command, the remaining commands will continue to be executed. 
	
options: -e
	make -e
	#The variable at the up level will override the one at the next level.

options: -w
	make -w
	#when Enter or leave a directory ,print the message.
	# --no-print-directory
options: -C
	enable option '-w'