It would be better to mail a letter of application to his advertiser ______ to call him.

A．It means "creating".
B．It means "producing".
C．It means "inventing".
D．It means "doing".

A．All the researchers doubt that X-rays can be produced by sparks at first.
B．X-rays produced in lab is just the same with those by lightning.
C．The result of the study is in expectation of every researcher.
D．The researchers detected X-rays in sparks of 1.5 million to 2 million volts.