rain would need a suffix if it was to be a verb. Rain is a noun by itself.
Rain is present tense. The past tense is rained.
The present tense of the verb 'was' is is.
Can is the present tense.
The present tense for the verb "have" is "have" for the pronouns I, you, we, and they, and "has" for the pronouns he, she, and it.
"Is" is the present tense form of the verb "to be" and "has" is the present tense form of the verb "to have."
Studied is not a present tense verb. It is the past tense of study (present tense).
The past tense for the verb "rain" is "rained".
Present tense.
Washes is the present tense.
* I am * you/we/they are * he/she/it is
The present tense is 'is'
But is not a verb and does not have a present tense.