写亿以上的数时，要先______，然后______位起读一级写一级．
写亿以上的数时，要先写亿级，然后从高位起读一级写一级．
故答案为：写亿级，从高．
What ___ to your good friend the day before yesterday? [ ]
A. was happened
B. happen
C. happening
D. happened
