Why does the Pasuk say "when Avraham came to Egypt," and not "when they came to Egypt"?
Rashi: Avraham hid Sarah in a box, in the hope that she would escape attention. However, when the tax-inspectors ordered him to open it, much to their surprise, they discovered her there. 1
Gur Aryeh: Although we find an earlier verse (12:10) that is also in the singular, "And Avraham went down," Sarah is not the subject of that verse. In our verse, Sarah is the subject, and it is therefore surprising that she is not referred to at its beginning.