Ctex in the r markdown problem

hi guys, i have met a problem and i need your help desperately!
when i open a r markdown under the ctex, i could get the result in the form of pdf. it just couldn't work it out. the specific error is as follows
it says' latex fail to compile (file name) see http://yihui.org/tinytex/r/#debugging for debugging tips.
and there is also a warning message as follows
warning message:
in has_crop_tools( ):
tool(s) not installed or not in PATH:ghostcrip
as a result, figure cropping will be disabled

it has already bother me for a really long time. and i don't know how to deal with that.
thank you guys!

This is a duplicate of this one