Use the following number scheme: $1-$ No current $2=$ low current $3=$ no current

The threshold frequency for a certain metal is yellow light.

NR$.3$ f bright orange light is shone on the metal surface, then the result is

$($a$)$

If dim UV light is shone on the metal surface, then the result is$\_($b$)$

If bright blue light is shone on the metal surface, then the result is

$($c$)$

If dim IR light is shone on the metal surface, then the result is$\_/$d$)$