一般现在时描述声音来源 — 英语选择题

放学回家路上，小美听到三种声音：闹钟 goes 'Tick-tock'，小狗 goes 'Woof'，小鸟 goes 'Tweet-tweet'。她想说：（1）闹钟正在发出声音；（2）鸟在树上唱歌。哪一组句子完全正确？A. The clock ticks. A bird sings in the tree. B. The clock ticking. A bird sing in the tree. C. The clock ticks. A bird singing in the tree. D. The clock tocks. Birds sings in the tree.