现在进行时：
Look!The dinosaur is falling down .
一般过去时：
The dinosaur fell down last night.用（often)改Look!The dinosaur is falling down此句~~often 常用于一般现在时，应该这样改：The dinosaur often falls down.那Yesterdayhedidhomeworkverycarefuly 用（always)和（now)改写……He always does his homework very carefully.He is doing his homework very carefully now.