His family are worried about him because they haven't ________ letters from him for a long time. A. accepted B. received C. written D. collected 答案:B聪聪在做作业时,不小心把墨水滴在了作业本上,有一道方程题被墨水盖住了一个常数.这个方程是2x-,怎么办聪聪想了想,便翻着书后的答案,此方程的解是x=-,他很快就计算好了这个常数,你认为这个常数是( )A.1B.2C.3D.4