the final two lines of shakespeares shall i compare thee to a summers day promises the subject of his sonnet
He promises immortality because he says that she shall live as long as the sonnet exists and as long as their love exists, and since the sonnet will exist forever just the same as their love, she will be metaphorically immortal.
IF THESE ARE THE OPTIONS FOR PF STUDENTS THE ANSWER WOULD BE
A. undying devotion.
B. immortality.
C. unfading youth.
D. an endless
B. IMMORTALITY