A 1. The Present Perfect is used to convey a sense of the end of the action (calling the register)
2. It is used to show that Arnold started crossing his eyes before he was addressed and was doing this for some time.
3. These are a time clause ("till you join us") and a conditional clause ("if there's anything..."), so we need to use the Present Indefinite (Simple) tense forms to talk about the future.
4.
1) If I were you, I should keep an eye on that boy. - Я бы на вашем месте следила за этим мальчишкой.
2) "I should give out paper and coloured pencils," said Miss Enderby, "as soon as you've called the register - "Я бы раздала бумагу и цветные карандаши, - сказала мисс Эндерби, - как только вы закончите перекличку".
3) One crumb of comfort, if comfort it could be called, remained with her. - У нее оставалось единственное утешение, если это можно было назвать утешением.
B
Words and phrases describing the children's actions
fixed their eyes upon Anne.
The children's faces were unmoved.
chorused the class obediently
the polite chorus
looked suitably crest-fallen
his pink face express his scorn of Miss Enderby
the forty-six tongues which had so far kept unnaturally silent began to wag cheerfully
the noise grew in volume as conversations became more animated
children ran across the room to see their distant friends
boys attacked each other
A child with birthday cards was displaying their beauties to an admiring crowd round her desk
was attempting to pull his shirt over his head, in order to show his friends a scar...
growing chaos
someone yelped with pain, there was a burst of laughter
Within a minute order had returned.
the children turned attentive eyes upon her.