罐体裂纹或焊缝开裂时，须（），裂纹末端钻止裂孔，两面焊。 A.截换 B.补焊 C.开

Most students feel like nervous before taking an important exam. Some feel dizzy or tiring, some have no appetite for food and other even suffer from sleep problems. All the symptoms have terrible effects in their exams. How can they get rid of these bad symptoms? Personal, it’s important to make a careful plan in advance to review what they have learned, what will help them reduce the pressure. Besides, they should arrange their time properly. They shouldn’t stay too late because only enough sleep makes them energetic and enable them to perform well in an exam. what’s more, a balanced diet can contribute to their perform in exams. They are supposed to eating various food such as eggs, milk, carrots, walnuts, etc.

一束与水平方向成50°角光线从空气射向平静的水平面（如图所示），画出这束光线的反射光线，以及它的折射光线的大致位置。

花生的种子是由花的______发育来的，胚是由花的______发育来的．

抗日战争时期的“三三制” * *

A．是敌后抗战的最好 * * 形式

B．既保证了工人阶级的领导地位和工农联盟为基础，又团结了广大的中间力量和一切赞成抗日民主的人士，孤立了顽固派

C．是抗日民族统一战线性质的 * * ，有利于结成最广泛的抗日民族统一战线

D．是以工人、农民为主，包括小资产阶级在内的工农民主 * *