Questions

The error is in first part. ‘Considering’ is a preposition that relates the facts to the principal and hence does not need to be followed by another preposition ‘about’. A preposition like ‘considering’ should be followed by a pronoun like ‘these’ in this case. The use of about is unnecessary and shall be omitted. The sentence indicates that the principal offered him a seat only after considering certain facts.

Leukocyte, commonly known as a white blood cell (WBC), is a major component in protecting the body against invading microorganisms and body cells with mutated DNA, and they clean up debris. 

B Lymphocyte also called as B-Cells or plasma cells produces the antibodies or immunoglobulins that bind to specific foreign or abnormal components of plasma membranes. This is also referred to as humoral (body fluid) immunity.

The Certificate of Deposit (CD) is a negotiable money market instrument and issued in dematerialised form or as a Usance Promissory Note against funds deposited at a bank or other eligible financial institution for a specified time period. (Usance Promissory Note has to be paid after certain time period).