题目

—The washing machine isn’t working.    —I used it this morning. It ______ fine then.[Z_xx_k.Com] A. is working        B. was working  C. works             D. has worked 答案：B15．下列关于细胞结构的说法，正确的是（　　）A．细胞膜的选择透过功能都与载体有关B．衰老细胞的细胞核体积减小、核膜内折C．核孔是DNA等大分子物质进出细胞核的通道D．细胞内细胞器的种类和数目影响细胞的功能