Sometimes, the words can express the same meaning but should be used in different situations. That is to say, the foreign students who study in intensive Mandarin course in China should learn to tell apart the differences between the similar words. 测量, 测试 and测验 is a group of words you should know the differences. 测量 indicates to measure the physical quantity like landform, location of things, temperature, speed and function and so on. Therefore, the scope of application is wide. You can say 测量风速and 测量密度.

However, 测试is to test, check or examine. The emphasis is to test, usually to check the conditions of people or things. You may often hear 测试水平and 测试仪器的精确度. And 测验 means to examine under certain standards and with some methods. It is very similar to 测试, but it often used to check the results of learning like 测验他们对词语的掌握.

The two adverbs 曾and 曾经are used to express the time “once”. The former one is applied to indicate the things have experienced once like 我曾去过一次. However, when you study in qualified Mandarin program, teachers would tell you that 曾经implies the actions, behaviors or conditions existed or happened in a period before. 过is usually placed after the verbs. For example, 他曾经做过小学老师. The basic usage of the two words are the same but 曾can be used together with the negative adverbs like 未 and 不. The latter has a wider scope of application than the former one which is often appear in written language.

During the process when you study Mandarin online, you may feel confused by the words 差别and 差异, both of which indicate the differences. The former one implies the differences in forms or contents like 毫无差别. 差别 has a wider scope of application because it can applied to indicate both the essential aspects and external phenomena. Used in written language, 差异 mainly for the essential aspects. We should say人类的遗传差异and 城乡差别逐渐缩小.