黄热病疫预防接种的有效期为自接种后第五日起，十年内有效，如果前次接种不满十年又经复种，自复种的当日起，十年内有效。( )

A lesson from the terrible drought(干旱) that hit some parts of southwestern China this year is that more anti-drought projects ______ built in the past years.

A．should be

B．should not have been

C．ought to have been

D．must be