单选题 When compiling electrical drawings and electrical technical documents, preference should be given to () among basic text symbols.

单选题 Auxiliary text symbols can be used on their own, or a two-letter symbol can be formed by placing a () after a single-letter symbol indicating the type of item.

单选题 In electrical diagrams, some special purpose terminals, wires, etc., are usually used in some special () combinations.

单选题 In general, basic text symbols cannot exceed two letters and auxiliary text symbols cannot exceed () letters.

单选题 The auxiliary text symbol for "alternating current" Is ().

单选题 The auxiliary text symbol for "Start" Is ().

单选题 The auxiliary text symbol for "Dc" Is ().

单选题 A simple figure with a definite meaning that must be combined with other figures to form the complete symbol of a device or concept, called ().

单选题 The auxiliary text symbol for "Protective grounding" Is ().