As of C++11, member function push_back is now overloaded with a version that takes a(n) ________. This allows the preceding call to push_back to take the storage allocated for the temporary string and reuse it directly for the new element in the vector. The temporary string will be destroyed when the function returns, so there’s no need for it to keep its content.

Prior to C++11 the following code created a temporary string object and passed it to push_back, which
then copied it into the vector:
vector; myVector;
myVector.push_back("message");
a. const pointer
b. rvalue reference
c. rvalue pointer
d. const reference

b. rvalue reference