“昨天”is very important. Usually Chinese past tense can be found in context, like“昨天”。 There is only one symbol word which can mark past tense in Chinese. That's “了”。 For example, 我累了（I was tired.）○ 我昨天累了（I was tired yesterday.）× 我昨天很/好/真累（I was tired yesterday）○ 你很/好/真漂亮（You are pretty.）○ 你很/好/真漂亮（You were pretty）○ 你昨天很/好/真漂亮（You were pretty yesterday）○ 你昨天漂亮了（You were pretty yesterday）× 你漂亮了（You were pretty）×

Chinese is differ to Europan language, by my experience Chinese have no past tense, if you want Highlight a Thing occurred in past time, such as"I was tired yesteday", you can say"我昨天很累/昨天我很累"， that have no tense changes. Actually, Chinese is a very open, easy, free language compared to most of others. Most difficult factor is Chinese character, you had better memorized about 1500 characters, but if you learn Chinese culture and history, you will find Chinese character have manifest Regulation to memorize.

There is no "tense" concept in Chinese, so we can forget about past tense, future tense...easy. Here are some example. 我昨天很累 I was tired yesterday. 我很累 I am tired The word "昨天" indicates a past event. In some cases, the "tense" is implicit, you need to have the whole paragraph for a correct translation.

Usually express in oral is "subject+time(+很(It just like the word "very".)+adjective". Example 1.我昨天生病了。(I was sick yesterday). 2.她昨晚很美.(She was pretty last night.).