在仪器设备的使用中，使用人员应详细了解使用说明书内容，熟练掌握仪器设备的性能和操作程

已知正方体ABCD-A₁B₁C₁D₁的棱长为1，则直线DA₁与AC间的距离为______．

阅读理解。

1. Mary is allowed to order her lunch from a small restaurant on the third Thursday of every month.

    During the month of November, she orders it on the ________.

A. 16th

B. 17th

C. 21st

D. 14th

2. January 8, 2007 will fall on ________.

A. Saturday

B. Sunday

C. Monday

D. Tuesday

3. The dates of the first Sundays of October, November and December are ________.

A. the 5th / the 1st / the 31st

B. the 5th / the 30th / the 3rd

C. the 1st / the 5th / the 3rd

D. the 1st / the 4th / the 2nd

4. During the month of December, Kate is learning to swim. She needs to attend lessons once a week.

   The day she can attend the most lessons is ________.

A. Sunday

B. Monday

C. Tuesday

D. Wednesday

5. Tom's birthday is on the 13th of December. The numbers of days from the date (not included) shown

    on the calendar until his birthday is ________.

A. 3

B. 13

C. 28

D. 30

请简述常用的两种光电检测器件的名称、特点、参数指标，及其适用的场合。

甲企业因基建需要竹签，与乙厂签订了一供货合同，合同约定，乙供应甲竹签100捆，每根竹签单价1元，未约定总价。乙如约按惯例供应竹签100捆，每捆100根，甲企业以自己认为每捆竹签为10根，现每捆竹签为100根为由，主张变更合同，遭乙企业反对，双方发生纠纷。对此纠纷如何处理

A．按重大误解处理

B．按合同解释处理

C．或按无效合同处理，或按合同解释处理

D．按无效合同处理

（）政治报告宣布，以粉碎“ * * ”为标志，“ * * ”宣告结束。

A.党的十大

B.党的十一大

C.党的十二大