Ce versus cela/ceci

Question

In the question...________ retarde le train, c'est la grève.What delays the train is the strike.... I wrote "Cela qui". Why is "cela" not acceptable?

Cécile Janty-Davies · Accepted Answer

Bonjour Harry,
I am afraid you are mixing your pronouns.
ce qui/ce que are relative pronouns as per lesson.
Wheras cela is a demonstrative pronoun.
Please take a look at the following lesson highlighting its use -
Ceci/Cela = this/that (French Demonstrative Pronouns)
Bonne Continuation !

Céline Pickard · Answer

Bonjour Joe,
In French, "lequel" cannot be used instead of "ce qui". However, "lequel" is interchangeable with "qui" after prepositions.
Take a look here below: 
qui or lequel
I hope this is helpful.
Bonne journée !

Mark Carter · Answer

needs to link to the object

Joe Neuman · Answer

Can "lequel" substitute ce qui

Cécile Janty-Davies · Answer

Bonjour Joe,
In which specific example?