More highways have been built in China，________it much easier for people to travel from one place to another.(2011·陕西)

A．making

B．made

C．to make

D．having made

两只白色家兔交配后， * * 下八只小兔，其中六只白色、两只黑色。若用D表示显性基因，d表示隐性基因，则所生黑色小兔的基因组成是

A．DD

B．Dd

C．dd

D．DD或Dd