问题
选择题
1.25×2.5×0.8×0.4=（1.25×0.8）×（2.5×0.4）这里运用了（ ）
A．乘法交换律
B．乘法结合律
C．乘法分配律
D．乘法交换律和乘法结合律
答案
1.25×2.5×0.8×0.4，
=（1.25×0.8）×（2.5×0.4），
=1×1，
=1．
故选：D．
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1.25×2.5×0.8×0.4=（1.25×0.8）×（2.5×0.4）这里运用了（ ）
A．乘法交换律
B．乘法结合律
C．乘法分配律
D．乘法交换律和乘法结合律
1.25×2.5×0.8×0.4，
=（1.25×0.8）×（2.5×0.4），
=1×1，
=1．
故选：D．
| Mr. Faugel was convinced that student nervousness had affected their scores; to reduce the anxiety of these students who had already been tested, he gave 22 of them a beta blocker before readministration of the test. Their scores improved significantly. The other 8 students (who did not receive the beta blockers) improved only slightly. Second-time test-takers nation-wide had average improvements which were similar to those in Faugel’s non-beta blocker group. Beta blockers are prescription drugs which have been around for 25 years. These medications, which interfere with the effects of adrenalin, have been used for heart conditions and for minor stress such as stage fright. Now they are used for test anxiety. These drugs seem to help test-takers who have low scores because of test fright, but not those who do not know the material. Since there can be side effects from these beta blockers, physicians are not ready to prescribe them routinely for all test-takers. |
According to the passage
A．all people can take beta blockers.
B．beta blockers am widely prescribed.
C．beta blockers work only on test anxiety.
D．beta blockers work only to improve test scores if the test-taker truly knows the material.