and作连词后面加逗号吗

I often _______ a letter to my pen friend. 1是 影子是怎样产生的?2是 为什么称为光 3是影子的特点 1 am 什么?a letter to my pen friend 英语翻译Not only farmers but also scientists have studied weather forecast.People,for many centuries and in all countries,have studied the weather and tried to make weather forecasts.Sometimes distant objects such as hills and tall trees seem to 一个梯形的花坛里,按3:2种植红、白月季花,该怎样种植?（梯形上底10米,下底15米,高6米）画出示意图.红月季面积? 种子植物受精卵的形成是在A.胚珠里 B.子房里 C.花粉管里 D.柱头上 怎样区分常见遗传病类型（说方法,不要只举例子）有x隐、x显、多基因、单基因等等各种各样,难道都是要背的么? 我将去找你,和你一起打篮球 用英语怎么说 黄色光是由什么色光和什么色光合成 红色光照在黄色物体上反射什么色光 有两个花坛,串红棵树的五分之一和月季花的三分之一相等,如果月季花再种12棵,两花相等,串红和月季各几别用方程解 情景交际． A Hi ,Lily Did you go to the concert last night?B Yes.A 1._______________________________?B I Went there with my parents.A 2.________________________________?B By car.A 3__________________________________?B It's moving.Many famous sin 以“走进阳光”为话题,写一篇关于散文的作文, 英语怎么说 影子的形成条件是什么? 用两个手电筒分别蒙上绿,黄玻璃纸,把光照在暗室中白墙的同一位置上,两种光重叠处光的颜色是?是黄绿色？ ____you enjoy the concert last night?A.are B.A____you enjoy the concert last night?A.are B.Am C.did D.Do I enjoy the concert last night; they played __ beautiful music.A.such B.such a C.so D.so a like things a party for would buy they to halloween连词成句 they would like ( ) buy things ( )a Halloween party they would like to buy things for a halloween party 改成一般疑问句和否定句 什么是简单随机抽样和分类抽样?举例说明它们之间的最主要区别. I would like to buy things for a Halloween party.这里为什么要填to buy? They wouid you like to buy things for a Halloween 请举例说明操作系统的分类情况 关于脸分类的举例我们选的研学的课题是：脸我将它分成5类,分别是：1五官精致又好看【赫本】2五官不精致但好看（耐看）【俊秀】3五官精致却不好看【?】4五官不精致也不好看【芙蓉JJ】5 和我同学玩用英语怎么说 有性生殖的植物却无性生殖有一些有性生殖的植物 在农业上却是无性生殖的 比如说哪些植物是在农业上发挥作用的 回答越多越好 Did you go( ) last Sunday .--Yes ,I went to the aquarium.A everywhere B anywhere C somewhere ___you ___ (listen) to the concert last night?横线中填什么有会的来!速求答案!急 怎样看天上的星星识别方向? 天上有几颗星星,他们分别叫什么?