least significant bit,and most significant bit if a,b are both binary bit. a=0, and b=0, what is least significant bit,and most significant bit of a+b, which means 0+0?
if c is the carry bit, and c=1, what is the least significant bit,and most significant bit of a+b when a=0,b=1

My thought is 0+0=0, thus least significant bit,and most significant bit are same, which is 0. and if C is carry bit, than a+b=1, then add carry bit, which is 10, so the the least significant bit is 0, and msb is 1..am I right? someone help
"Most significant bit" is a concept that depends on the size of the machine word. If $a + b + c = 10$ and the machine word has size $64$, then the MSB is $0$. It is $1$ only if the machine word has size $2$. (Under your definition, the MSB is always $1$, unless the number is $0$, in which case it is undefined.)