353×22的积大约是______(填整千数)积是______位数.
353×22≈400×20=8000,积是4位数.
故答案为:8000,4.
These flowers should not be watered too _____, once _____. [ ]
A. long; every other day
B. often; every fourth day
C. soon; every two days
D. frequently; each five days
绝缘靴的工频耐压试验周期是6个月