Mark correct statements

Question $1$ Select one or more:

a$.$

Inductive proximity sensors are mostly used for long$-$range detection of small objects

b$.$

Optical sensors require clean environment

c$.$

PLC does not hold any control program and is being used only to switch physical outputs, according to the program commands from central PC$/$SCADA$.$

d$.$

Optical proximity sensors can detect only metal objects