A space is an implied AND in a search string, which means that it acts as a logical operator that returns events that match both terms on either side of the space2. For example, status=200 method=GET will return events that have both status=200 and method=GET2. Therefore, option B is correct, while options A, C and D are incorrect because they are not implied by a space in a search string.

Reference:https://docs.splunk.com/Documentation/Splunk/8.0.3/Pivot/IntroductiontoPivot

Explanation
The command sourcetype=access_combined | transaction JSESSIONID does three things:
It filters the events by the sourcetype access_combined, which is a predefined sourcetype for Apache web server logs.
It groups the events by the field JSESSIONID, which is a unique identifier for each user session.
It creates a single event from each group of events that share the same JSESSIONID value. This single event will have some additional fields created by the transaction command, such as duration, eventcount, and startime.
Therefore, the statements B, C, and D are true.

Reference: https://docs.splunk.com/Documentation/SplunkCloud/8.0.2003/Knowledge/Defineeventtypes When multiple event types with different color values are assigned to the same event, the color displayed for the events is determined by the priority of the event types. The priority is a numerical value that indicates how important an event type is. The higher the priority, the more important the event type. The event type with the highest priority will determine the color of the event.