Tough question, I would suggest using Google maybe, or just plain out asking your science teacher.
16 is C
17 is E
18 is B
19 is A
20 is D
hope this helps :)
The complete reaction along with intermediates is given below, with each step highlighted in different color.
Step 1: In this step an acidic proton at alpha position is abstracted from lactone moiety and corresponding enolate is formed, which is resonance stabilized. Both structures are shown. In this case LDA (<span>Lithium diisopropylamide) acts as a base.
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Step 2: The enolate formed attacks on Methyl Iodide, as Iodide being greater in size is a good leaving group and alpha methyl moiety is generated.
Step 3: This step is acid catalyzed Bromination. Bromine is added at alpha position.
Step 4: This is elimination reaction and is according to <span>Hofmann's Rule. Here less substituted alkene is generated.</span>