下面说法中正确的是（ ）
A．速度变化的运动必定是曲线运动
B．加速度恒定的运动不可能是曲线运动
C．加速度变化的运动必定是曲线运动
D．做曲线运动的物体速度方向必定变化
A、匀变速直线运动的速度发生变化，不是曲线运动，A错误；
B、平抛运动的加速度恒定，是曲线运动，B错误；
C、变加速直线运动的物体做的不是曲线运动，C错误；
D、做曲线运动的物体的加速度不为零，故速度必然发生变化，D正确；
故选：D
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| Tina and Tara are twin sisters. They look 1 , but they also have some differences. Mr. Black is their old grandfather. One day, he came to see his two granddaughters 2 two gifts. When he came into the house he saw Tina and 3 her one gift. After a while, when he got into the garden he saw 4 granddaughter-"Tara". In fact, that was Tina. When he gave the other gift to her, she said, "you have given me one." "No, I gave a gift to your 5 -Tina." "Oh, my grandpa, I am Tina." Just then, Tara came into the garden, too. "Now, grandpa, can you tell me the differences 6 us?" "'No, I can't. Can you 7 me?" "Yes, look, Tara is a little taller 8 me. Her hair is longer and curlier, then 9 . Now grandpa, can you see?" "Yes, now I can tell you 10 Tara. Tara, here is the gift for you." "Thank you for your gift, grandpa." With the words, they all laughed happily. | ||||
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