[简答题]普规规定：四显示自动闭塞区段进站色灯信号机显示一个绿色灯光和一个黄色灯光的含义是（）。

Passage Three
The development of Jamestown in Virginia during the second half of the seventeenth century was closely related to the making and using of bricks. There are several practical reasons why bricks be came important to the colony.
Although the forests could initially supply sufficient timber, the process of lumbering was extremely difficult, particularly because of the lack of roads. Later, when the timber on the peninsula had been depleted, wood had to be brought from some distance. Building stone was also in short sup ply. However, as clay was plentiful, it was inevitably that the colonists would turn to brickmaking.
In addition to practical reasons for using brick as the principal construction material, there was also an ideological reason. Brick represented durability and permanence. The Virginia company of London instructed the colonists to build hospitals and new residences out of brick. In 1662, the town Act of the Virginia Assembly
A. The reasons for brickmaking in Jamestown.
B. The cause of the failure of Jamestown.
C. The laws of the Virginia colonists.
D. The problems of the early American colonies.

某安装工程公司承接架空蒸汽管道工程。管道工程由型钢支架工程和管道安装组成。
项目部根据现场实测数据，结合工程所在地的人工、材料、机械台班价格编制了每10吨型钢支架工程的直接工程费单价，经工程所在地综合人工日工资标准测算，每吨型钢支架人工费为1380元，每吨型钢支架工程用各种型钢1.1吨，每吨型钢材料平均单价5600元，其他材料费380元，各种机械台班费400元。
由于管线需用钢管量大，项目部编制了两套管线施工方案。两套方案的计划人工费15万元，计划用钢材500吨，计划价格为7000元/吨。甲方案为买现货，价格为6900元/吨，乙方案为15天后供货，价格为6700元/吨。如按乙方案实行，人工费需增加6000元，机械台班费需增加1.5万元，现场管理费需增加1万元，通过进度分析，甲、乙两方案均不影响工期。
工程进行过程中，发生了以下事件：
事件一：在采购一批管道焊接用的共2吨低合金耐热钢焊条时，施工单位按建设单位指定的合格供应商确定了焊材供应商。施工单位对供应商首次送货的0.5吨焊条进行抽样检测合格。对后两次送货的其余1.5吨焊条均未检测，接收后直接用于焊接。在施焊过程中发现焊缝出现大量延迟裂纹。建设单位与监理工程师对焊条重新进行抽样检测，确认为不合格。为之建设单位要求施工单位承担全部责任，所有用此供应商的焊条进行焊接的管线全部重新组焊。施工单位认为供应商是建设单位指定的，应由建设单位承担责任。
事件二：安装工程公司项目部在工程施工自检时，发现架空蒸气管道坡度、排水装置、放气装置、疏水器安装均不符合规范要求。检查组要求项目部立即整改纠正，采取措施，确保质量、安全、成本目标，按期完成任务。
事件三：建设单位在工程后期组织进行工程质量大检查，对施工单位的一项通过检查验收合格的隐蔽工程进行重新检验，发现不符合质量验收标准。建设单位要求施工单位返工并支付检验费用。