cannot find -l boost_thread

[noobgrow]

Here is what I met when I do 'make ':

CXX .build_release/src/caffe/proto/caffe.pb.cc
AR -o .build_release/lib/libcaffe.a
LD -o .build_release/lib/libcaffe.so.1.0.0-rc3
/usr/bin/ld: cannot find -l　boost_thread
collect2: error: ld returned 1 exit status
Makefile:568: recipe for target '.build_release/lib/libcaffe.so.1.0.0-rc3' failed

I have no idea about how to find the boost_thread.

I found libboost_thread is in usr/lib ,and added it to ./bashrc
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib
I also tried reinstall boost,then copy to usr/lib

but question still resist.How can I solve this?
Thank you in advance!