Be  to + infinitive :

1/ To convey orders and instructions:

Ex:

• At the end of the week , all students are to take two exams.

• No one is to leave the building without  my permission.

• You are to stay here till I return.

2/ Official arrangements or plans:

Ex:

• The prime minister is to visit Canada next week.

• A new train line is to be built. (Passive form)

3/Past forms :

A/ Was/were  to + infinitive for things that happened:

Ex:

• He was to travel to Paris. ( He planned the travel  and he did travel.)

B/ Was/were to + perfect infinitive for unfulfilled plans:

Ex:

• The manager was to have made a historic speech last week, but he was taken ill. (He didn't make the speech.)

• The meeting was to have been held last Monday, but it was put off due to unforeseen circumstances.(Passive form)

4/ Be to+ infinitive in if-clauses: used to talk about preconditions for something to happen.

Ex:

• If Ali is to succeed, he needs to study hard.

• If we are to solve the world's pollution problems, we must address environmental issues now.

**** Note:

We don't use be to +infinitive to talk about events that can't be controlled by people:

Ex:

• There are fears that sea level  will rise catastrophically in the next 50 years. ( Not is to be rise......)

The present perfect and the present perfect continuous :

A/

§ We use the present perfect continuous  rather than present perfect simple when we draw a conclusion from what we can see and hear, ect. This form is usually used to complain and criticise.

Ex:

-You have been working all night. You look exhausted.

- Someone has been messing around with my computer.

B/

§When we talk about the result of circumstances or an activity, we use the present perfect rather than the present perfect continuous. When the focus is on the process we use either the present perfect or the present perfect continuous .

Ex:

- The prices of houses have increased by 10%.(The focus is on the result)

- The prices of houses have been increasing recently. (or “have increased”-The focus is on the process-)

C/

§ The present perfect continuous emphasises that an activity is ongoing or repeated.

Ex:

-She has been reading the book all day.

§The present perfect suggests that an activity happened only once or on a specified number of occasions

-Sam has represented the company at 35 forums so far.