Claim the theory wrong?
The lecturer claims that the ~ theory to be wrong
The lecturer claims that the ~ theory wrong

Which one is natural?
and what words can I use instead claim in this case
contend? sustain?
help me

Question

Claim the theory wrong?
The lecturer claims that the ~ theory to be wrong
The lecturer claims that the ~ theory wrong

Which one is natural?
and what words can I use instead claim in this case
contend? sustain? 
help me

Answer

You must use 'to be'. So 'the theory is wrong'.

'Claim' is perfectly okay. Often people use 'argue' in this context.

So 'The lecturer argues that the theory is wrong."