If avian flu H5N1 gained the ability to move from person to person, it could cause a ______.

A．The sailor spoke several languages.
B．The parrot knew many bad words.
C．The man had a very big vocabulary.
D．The guests often embarrassed the bird.

A．The man saw Mark on the street two months ago.
B．The woman had forgotten Mark’s phone number.
C．The woman made a phone call to Mark yesterday.
D．Mark and the woman had not been in touch for some time.