obligation in the past:
I had to wear a school uniform when I was a child.
No obligation in the past: We didn’t have to go to school on Saturdays
must*
changes to 'had to'
should have + Ved(V3) / shouldn’t have + Ved(V3)
a past action which didn’t happen: the advice / regret is too late
You should have gone to bed earlier, now you have missed the train.
A past action which didn’t happen: the advice / regret is too late: You shouldn’t have taken that job., it was
Questions:Should I read this book?
Do I have to read this book?
The modal verb must is not used in questions, instead of it we use have to. Notice: in scientific style the frequently used modal verb is should. We can’t say: This reaction must occur at high temperature. We must say: This reaction should occur at high temperature.
The modal verbs “must”and “have to” are mainly used in everyday speech contexts.
Vocabulary acyclic алифатический (ациклический)
a homologous series гомологический ряд
ethylene этилен
International Union of Pure and Applied Chemistry Международный совет по теоретической и прикладной химии
thane этен
on the largest scale в больших масштабах
industrially на производстве
to draw изображать
combustible легковоспламеняющийся
odorless без запах
propene пропен
butene бутен
room temperature комнатная температура
a waxy solid воскообразное твердое тело
allylic аллиловый
to serve as служить в качестве
a feedstock исходное сырье
to participate участвовать
petrochemical industry нефтехимическая промышленность
polymerization полимеризация
alkylation алкилирование
a wide variety of большое число
reactivity реакционная способность
higher alkenes высшие алкены
approximately примерно
a liquid жидкость
safety regulations техника безопасности
to observe соблюдать
a glove перчатка
to pass an exam сдавать экзамен
to explode взрываться
to break the rule нарушать правило
to dilute разбавлять
boomerang effect обратный эффект
to follow the rule соблюдать правило
a laboratory assistant лаборант
physical state физическое состояние
molecular mass молекулярная масса