Given that sin A=5/13 and 0°≤A＜ 360°, what are all possible values of cos A ？
A. -5/13 only
B. -5/13 and 5/13
C. 12/13 only
D. -12/13 only
E. -12/13 and 12/13
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The sum of 2 numbers is 90. The smaller number is 50 less than the larger number. What is
A. 20
B. 40
C. 45
D. 70
E. 80
In each of the 13 trials, how did the magnitude of the electrical force exerted by Sphere
A. The magnitude of the electrical force exerted by Sphere X on Sphere Y was greater than the magnitude of the electrical force exerted by Sphere Y on Sphere X.
B. The magnitude of the electrical force exerted by Sphere X on Sphere Y was less than the magnitude of the electrical force exerted by Sphere Y on Sphere X.
C. The magnitude of the electrical force exerted by Sphere X on Sphere Y was the same as the magnitude of the electrical force exerted by Sphere Y on Sphere X.
D. Cannot be determined from the given information
According to Student 2, as the force of gravity exerted by Earth on a block increases, will the average speed of the block increase or decrease, and why？
A. Increase, because the weight of the block will increase.
B. Increase, because the weight of the block will decrease.
C. Decrease, because the weight of the block will increase.
Decrease, because the weight of the block will decrease.
问：我是新手，觉得钢笔工具很不好控制，有什么好的方法或者技巧呢？
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