Выберите нужные ответы: 1. They don't have to/doesn't have to do any chores. 2.We have to/has to switch off our mobile phones in class. 3.Roma has to/have to get ready for school now.

1. They don’t have to do any chores.

2. We have to switch off our mobile phones in class.

3. Roma has to get ready for school now.

Надеюсь

Все изотопы одного элемента имеют одинаковый заряд ядра. Обычно изотоп обозначается символом химического элемента, к которому он относится, с добавлением верхнего левого индекса, например, 12 C, 222 Rn. Все изотопы одного элемента имеют одинаковый заряд ядра, отличаясь лишь числом нейтронов. Обычно изотоп обозначается символом химического элемента, к которому он относится, с добавлением верхнего левого индекса, означающего массовое число (например, 12C, 222Rn).  

Обьяснение:

Пример:

Углерод.Изотоп 12C называется легким, 13C тяжелым, а 14C радиогенным.

A student smart card is a very useful tool, controlled by electronic systems, that can be used in a lot of different ways.  It can be used by students, as well as staff members to access college buildings and ensure the facility's safety as only cardholders will be able to enter. The same goes for other places such as libraries (you can either use it to enter the library itself or, for example, borrow and return books) and any kind of accommodation (dormitories in our case). Another usage the smart card has is that similar to what we use our credit cards for - cashless payment. You can use it to pay for anything you can find on campus: make photocopies or scan and print out documents, buy food and drinks from vending machines or order favourite dishes at any available catering facility and use your smart card to pay for it. As you can see, opportuinities are endless and make student life much more comfortable and accessible.