*** WARNING L2:REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL:
*** WARNING L2:REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL:MAIN MODULE:C:KEILC51LIBC51S.LIB
*** WARNING L2:REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL:MAIN
MODULE:C:KEILC51LIBC51S.LIB C_INIT)
ADDRESS:080DH
Program Size:data=13.0 xdata=0 code=265
creating hex file from "lesson1-11"...
"lesson1-11" - 0 Error(s),3 Warning(s).怎么解决这些警告