How do these definitions match research, require, process, and respond?

Question

Match the definitions to process, require, respond, research. If no word fits, write “-”.

1. to investigate systematically;
2. to specify as compulsory or make something necessary;
3. to differ in size, amount, degree, or nature;
4. to buy or obtain an asset or object;
5. to perform a series of mechanical or chemical operations on something;
6. to say something in reply.

Explanation

Research means to investigate systematically. Require means to demand something or make it necessary or compulsory. Process means to treat something through a series of mechanical or chemical operations. Respond means to reply.

Definition 3 describes vary, and definition 4 describes acquire. Those verbs are absent from the list, so put “-” in rows 3 and 4.