Quiz #1

The Answer is A.

The numbers in Lightning Experience uses JavaScript's Number type to determine the max and min number of digits, which means that they are limited to the MAX_SAFE_INTEGER and MIN_SAFE_INTEGER precision (which is about 16 digits).

The Answer is D. 

Validation rules don't apply when you create new records with the Quick Create (Create Records with Quick Create).
If you want to deactivate it, then you need to visit Setup > Customize > User Interface and uncheck the box for "Show Quick Create."

The Answer is B.

Opportunity Contact Roles does not support apex triggers. There is an idea for this - Make Opportunity Contact Role a First Class Object
Salesforce have delivered new customization options in Winter '20. Opportunity contact role customization options give you the flexibility to track and attribute revenue to roles, titles, and individuals. With custom fields and page layouts, validation rules, and Apex triggers, you can design an Opportunity Contact Role to match your specific sales and reporting processes. Please refer to the following article for more information: Contacts: Customize Opportunity Contact Roles for Better Tracking and Reporting.

You can use the code below to determine the list of objects that do not support apex triggers:

for (Schema.SObjectType soType : Schema.getGlobalDescribe().values()) {
  final String soTypeJSON = JSON.serialize(soType.getDescribe());
  Map<String, Object> m = (Map<String, Object>) JSON.deserializeUntyped(soTypeJSON);
  if (false == m.get('triggerable')) {
    System.debug(LoggingLevel.Error, String.format('{0}({1})', new String[] { 
        '' + m.get('label'), 
        '' + m.get('name') 
    }));
  }
}