一根头发丝的直径约8.2µm，合____m．正常平静时的一次心跳所需的时间大约是0.8____ ．如图所示，如果尺子的单位是cm，木板的长度是____ cm．

    Li Ming wants to buy some gifts for his mother and cousin in China. He goes to a shop. He buys two dresses for his cousin and some dishes for his mother. Now he needs some boxes. Jenny gives the boxes to Li Ming. Li Ming says thanks to Jenny and writes letters to his mother and cousin. Then Li Ming goes to the post office and buys four stamps. He thinks that his mother and cousin will like the gifts. He walks back to his house. He feels happy.

要使马铃薯和甘薯高产应当注意使用哪种无机盐（　　）