What is the difference between two sentences? You ____be a bit tired.Why not stop to rest? You ____be so tired that you had to stop to rest. The word in the blank is MUST and CAN'T.Why?What is the difference between two sentences?

Family As is vividly shown in the picture,the word family represents three people,who are father,mother and I.When I was young,father was the most important person in my family.Where there is my father,there is the sense of security.He applied himself year in year out to the work for providing my family with a better living. While my mother did her utmost to assist my father in family chores.She made sure I eat well and wear warm,rendering my family brighten and happier,much the way an umbrella fends off wind and rain. As times passes by, I grow up little by little.In the lovely and violent contrast with me, my parents become older and weaker. What’s worse, some diseases go down to them, my dad even lean heavily on his crutches. I come to realize that my aged parents are no longer free to hold up the family. It’s high time for me to take over the responsibility and shoulder the burdens. The pictures reflect a truth that Word Family means ‘dad and mom, I love you!’ Nothing can be compared, I think, family is a warm harbor whose door is eternally open for me wherever I go.Therefore, respecting them is of vital importance. Not only should we relate to them, but also endeavor to avoid setting off the conflicts. None the less, what we can do is to go to great lengths to spare more time to accompany them and sharing more houseworks. There is a long way to go, but the reward will paid for the price.

What do you think about <NEW CONCEPT ENGLISH> I'm kind confused about the grammars or sentences（like 'put sand in the wheels of','much the way','year in year out'...） in this book is standard enough.What native English speker think about this ?Do you use it in your daily talk and wrting?Our english textbooks are not written by native english speaker.The authors are mostly Chinese.C onsequently we have learned Chinese English,which is designed to deal with exams. So although we have learned English for a long time,many of us still can't apply it well.So what I confuse about is how to write an natural article?That 's why I study this book.