After one month of pregnancy,the embryo's $A$ is formed. By the end of the $B$ month of pregnancy,the foetus develops limbs and digits. By the end of $C$,most of the major organ systems are formed,for example,the limbs and external genital organs are well-developed. By the end of $D$,the body is covered with fine hair,eyelids separate,and eyelashes are formed. Here $A$ and $D$ refer to:

• A
  $A-$heart,$B-$second,$C-$first trimester,$D-$second trimester
• B
  $A-$heart,$B-$second,$C-$first month,$D-$second month
• C
  $A-$heart,$B-$second,$C-$first week,$D-$second week
• D
  $A-$heart,$B-$second,$C-$first trimester,$D-$second trimester (Note: The original question options were incomplete/incorrect; based on $NCERT$,$A$ is heart,$B$ is second month,$C$ is first trimester,$D$ is second trimester.)